Term "plastics" is a general term for all types of plastics. Their applications are widespread, therefore, classification methods vary. Broadly speaking, they can be divided into two categories based on their uses: general-purpose plastics and engineering plastics. General-purpose plastics include polyethylene (PE), polypropylene (PP), polystyrene (PS), modified polystyrene (e.g., SAN, HIPS), polyvinyl chloride (PVC), etc. These are the most widely used materials in daily life, with low performance requirements and low cost. Engineering plastics refer to plastics with industrial qualities such as those used for mechanical parts or engineering structures. They possess superior mechanical properties, electrical properties, resistance to chemical environments, and resistance to high and low temperatures. In engineering technology, they can even replace certain metals or other materials. Common examples include ABS, polyamide (PA, commonly known as nylon), polycarbonate (PC), polyoxymethylene (POM), acrylic glass (PMMA), and polyester resins (such as PET, PBT), etc. The first four have developed the fastest and are internationally recognized as four major engineering plastics.
Based on their processing properties during heating, plastics can be divided into two main categories: thermosetting plastics and thermoplastic plastics. Thermosetting plastics solidify and harden upon heating, their molecular structure transforming into a network or three-dimensional form. Once hardened, they cannot be softened again even with heating. These materials are characterized by their hardness, good heat resistance, relatively stable dimensions, and insolubility in solvents. Common examples include phenolic resin (PF), epoxy resin (EP), and unsaturated polyester (UP). Thermoplastic plastics soften and melt under heating conditions, solidify upon cooling, and can be repeatedly processed while maintaining their plasticity. Processing involves physical changes.
Common examples include polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polystyrene (PS) and its modified varieties, ABS, nylon (PA), polyoxymethylene (POM), polycarbonate (PC), and plexiglass (PMMA). These plastics have relatively simple molding processes under certain plasticizing temperatures and appropriate pressures, their products possess various physical and mechanical properties.

Thermoplastics we encounter today are all thermoplastics, which can be divided into two main categories: crystalline plastics and amorphous plastics. Crystallization refers to property of a polymer to rearrange itself in an orderly manner from a disordered molten state to a solidified state. Plastics with this property are called crystalline plastics. Conversely, those without this property are called amorphous plastics, or non-crystalline plastics. Crystalline materials have a relatively clear melting point. When processing temperature reaches melting point, they enter a viscous flow state, polymer viscosity decreases rapidly, and irreversible plastic deformation occurs. Amorphous plastics, on the other hand, do not have a clear melting point as they transition from a solid state at room temperature to a viscous flow state upon heating. Generally, opaque or translucent plastics are crystalline plastics, such as polyethylene, polypropylene, polyoxymethylene, polyamide, and polyester; while transparent plastics are amorphous plastics, such as polystyrene, polycarbonate, polymethyl methacrylate (plexiglass), and polysulfone. Of course, there are exceptions, such as ABS, which is an amorphous plastic but is opaque.

a. Flowability: Different forms of thermoplastics have different processing properties, shrinkage properties, physical and mechanical properties.
Generally speaking, for crystalline plastics, when processing temperature is higher than their melting point, their flowability is better, and they can quickly fill cavity, requiring less injection pressure. Amorphous plastics have poor flowability, therefore, injection speed into cavity is slower, and they require higher injection pressure. Therefore, in mold design, a reasonable runner system size can be designed based on flowability of plastic. This avoids material waste due to an overly large runner system size, which also prolongs injection molding cycle; on the other hand, it avoids difficulties in filling and holding pressure due to an overly small runner system size. Of course, there are exceptions, such as polystyrene, which, although an amorphous plastic, has excellent flowability. Indicators reflecting flowability typically include melt flow index (MFR) and apparent viscosity. MFR (Mean Fluid Rate) refers to mass of melt flowing out of a standard capillary every 10 minutes in a melt flow rate meter under specific temperature and load conditions; its unit is g/10min. For polymers, under typical injection molding conditions, their flow behavior generally does not obey Newton's law of flow and is considered non-Newtonian fluid. Ratio of their flow shear stress to shear rate is called apparent viscosity. Apparent viscosity is not a constant at a given temperature; it varies with shear stress, shear rate, and even time in some cases.
b. Shrinkage: Thermoplastics undergo varying degrees of volume shrinkage from molten state to solidified state. Crystalline plastics generally exhibit a larger shrinkage rate and shrinkage range than amorphous plastics and are more susceptible to effects of molding processes. Shrinkage rate of crystalline plastics is generally between 1.0% and 3.0%, while that of amorphous plastics is between 0.4% and 0.8%. For crystalline plastics, post-crystallization should also be considered, as they can continue to shrink at room temperature after demolding. Amount of post-crystallization depends on thickness of product and ambient temperature; the thicker product, the greater post-crystallization.
Table 2-1 Molding Shrinkage Rate of Common Plastics

 

Note: Parameters marked with * are company recommended values.
c. Rheology: Rheological properties of polymers refer to relationship between stress, deformation, deformation rate, and viscosity during processing. This involves influence of temperature, pressure, time, molecular structure, molecular weight, and its distribution on these factors. Based on rheological properties of plastics, they can be divided into shear-sensitive materials and heat-sensitive materials. The stronger dependence of viscosity on shear rate, the faster viscosity decreases with increasing shear rate; this type of plastic is shear-sensitive. Common shear-sensitive plastics include ABS, PS, PE, PP, POM, etc. If melt viscosity is more dependent on temperature, the faster viscosity decreases with increasing temperature, this type of plastic is heat-sensitive. Common heat-sensitive plastics include PC, PA, PMMA, etc. For polymers, shear rate affects viscosity of both materials mentioned above. Increasing shear rate can reduce melt viscosity to varying degrees, causing a "shear thinning" phenomenon. Therefore, when designing runner systems, a larger runner size does not necessarily mean a smaller pressure drop. A appropriately smaller runner size can increase melt shear rate, reducing viscosity and further decreasing pressure drop. This effect is more pronounced for shear-sensitive materials. A smaller gate size can increase melt shear rate, generating significant frictional heat, resulting in a significant rise in melt temperature and a decrease in melt viscosity, thus increasing fluidity. Therefore, using a small gate is often successful for shear-sensitive plastics. However, when product wall thickness is large, gate size should be appropriately increased to extend solidification time of gate, taking into account pressure holding.
d. Orientation Effect: Another factor affecting product performance is orientation effect of plastic melt during flow. Under action of external forces, macromolecules of plastic melt are stretched and aligned parallel to each other along flow direction. This alignment cannot be eliminated before plastic cools and solidifies, freezing into solid product and forming orientation effect. Orientation effects weaken the overall integrity of a product, manifesting as inconsistencies in physical and mechanical properties across different directions. They can also lead to uneven shrinkage in various directions, potentially causing warping and deformation. Based on form and nature of forces acting on macromolecules in melt, orientation can be categorized into "flow orientation" under shear stress and "tension orientation" under tension. Factors controlling orientation include: Decreasing melt and mold temperatures enhance orientation effect; increasing injection pressure increases shear rate and shear stress, thus strengthening orientation effect; thinner products exhibit a stronger orientation effect; larger gate sizes intensify orientation effect.
Sometimes, special measures are taken to enhance orientation effect, improving tensile and flexural strength in orientation direction. Examples include stretched films and hinges.

Polyethylene is the most produced and commonly used plastic in daily life. It is characterized by its softness, non-toxicity, low cost, and ease of processing. Injection molding materials are milky white granules. Molecular formula is:

 

Due to its C-C bond structure and lack of side groups, it exhibits good flexibility and a regular, symmetrical molecular arrangement, making it a typical crystalline polymer.
Polyethylene is relatively easy to burn, emitting a paraffin-like odor when burning. Flame is yellow at the top and blue at the bottom, melting and dripping, and continues to burn after being removed from flame.
Currently, the two most widely used PE materials are HDPE and LDPE.
2.3.1 Basic Properties of HDPE and LDPE
HDPE (high-density polyethylene, commonly known as rigid soft polyethylene) has fewer branches in its molecular structure, a relative density of 0.94 g/cm³~0.965 g/cm³, and a crystallinity of 80%~90%. Its most prominent properties are excellent electrical insulation, good wear resistance, water impermeability, and chemical resistance; it is almost insoluble in any solvent at 60℃; and it has good low-temperature resistance, remaining flexible even at -70℃. Its main disadvantages include poor resistance to sudden temperature changes, low mechanical strength, and low heat distortion temperature. HDPE is mainly used to make blow-molded bottles and other hollow products, and secondarily for injection molding to make turnover boxes, stopcocks, small-load gears, bearings, and electrical component supports.
LDPE (low-density polyethylene, commonly known as soft polyethylene) has more branches in its molecular structure, with a density of 0.910 g/cm³ to 0.925 g/cm³ and a crystallinity of 55% to 65%. It is easily permeable to air and moisture, has excellent electrical insulation and chemical resistance, and its flexibility, elongation, impact resistance, light transmittance are better than HDPE. Its mechanical strength is slightly lower, and its heat resistance is poor, not resistant to light and heat aging. It is widely used for extruded packaging films, sheets, packaging containers, wire and cable sheathing, soft injection molded and extruded parts.
Similarities in performance between HDPE and LDPE: Both have low water absorption, so drying is not required before molding. Polyethylene is a shear-sensitive material; its viscosity is more significantly affected by shear rate. Polyethylene has a relatively high shrinkage rate and a strong directional tendency, making finished product prone to warping and deformation. Since polyethylene is a crystalline polymer, uniformity of its crystal structure directly affects density distribution of product. Therefore, cooling water distribution in mold should be as uniform as possible to ensure uniform density, guarantee dimensional and shape accuracy of product.
2.3.2 Considerations for mold design:
Polyethylene molecules exhibit orientation, which leads to a greater shrinkage rate in orientation direction than in perpendicular direction, causing warping, twisting, and deformation, as well as affecting product's performance. To avoid this, careful attention should be paid to determining gate location and selecting appropriate shrinkage rate during mold design. Polyethylene is soft and smooth, making it easy to demold. For products with shallow grooves on sidewalls, forced demolding can be used. Due to good fluidity of polyethylene, depth of venting grooves should be controlled below 0.03 mm.

Polypropylene (PP, commonly known as flexible polypropylene) is polymerized from propylene, with molecular formula:

 

It is a crystalline polymer, characterized by its light weight, non-toxicity, and odorless nature. It also possesses corrosion resistance, high temperature resistance, and high mechanical strength. Injection-grade polypropylene resin is white, waxy granules.
Polypropylene is easily flammable, with a yellow upper flame and a blue lower flame, emitting a small amount of black smoke and melting and dripping. It continues to burn after being removed from the flame, emitting a petroleum odor.
Polypropylene is broadly classified into two types: homopolymer polypropylene and ethylene-propylene copolymer with improved impact resistance. Copolymer polypropylene products exhibit improved impact resistance compared to homopolymer polypropylene.
2.4.1 Main advantages of PP performance:
Due to its good fluidity at melting temperature, it has a wider range of molding processes and less anisotropy than PE, making it particularly suitable for manufacturing various simple shapes. Surface gloss, dyeing effect, and resistance to external scratches are superior to PE materials. Among general-purpose plastics, PP has the best heat resistance. Its products can be sterilized by boiling at 100℃, making it suitable for tableware, kettles, and medical devices requiring high-temperature sterilization. Heat distortion temperature is 100℃~105℃, allowing for long-term use above 100℃. It has high yield strength and a very high flexural fatigue life. PP hinges, with appropriate thickness (e.g., 0.25~0.5mm), can withstand 70 million folds without significant damage. It has a relatively low density, making it one of the lowest density plastics known. See Appendix Table 2-2 for density range of common plastics.
Table 2-2 Density Ranges of Common

 

2.4.2 Main disadvantages of PP properties: As a crystalline polymer, its molding shrinkage rate is greater than amorphous polymers such as PS, ABS, and PC. During molding, its dimensions are easily affected by temperature, pressure, and cooling rate, resulting in varying degrees of warping and deformation. Depressions are prone to occur at thickness transitions, making it unsuitable for manufacturing products requiring high dimensional accuracy or prone to deformation defects.
It lacks rigidity and is unsuitable for use as load-bearing mechanical components. In particular, notches on product are highly sensitive to stress, so sharp corners should be avoided in design. It has poor weather resistance. Under sunlight, it is easily affected by ultraviolet radiation, which accelerates plastic aging, causing product to harden, crack, fade, or migrate.
2.4.3 Mold Design: Due to its large molding shrinkage rate, the gate location should be selected to ensure that melt fills cavity in a relatively balanced flow order, ensuring consistent shrinkage in all directions. For products with hinges, attention should be paid to selection of gate location, requiring melt flow direction to be perpendicular to hinge axis. Due to good fluidity of PP, depth of venting groove should not exceed 0.03mm.

Polystyrene (PS, GPS, commonly known as general-purpose PS or hard plastic) is an amorphous, transparent thermoplastic. It is first produced by addition reaction of benzene and ethylene to obtain ethylbenzene, from ethylbenzene to obtain styrene, finally from addition polymerization of styrene to obtain polystyrene. Chemical structural formula is: Polystyrene is easily combustible, with an orange-yellow flame, producing thick black smoke and char, softening, bubbling, and emitting a styrene monomer odor.
2.5.1 Main advantages of PS properties:
Good optical properties. Its light transmittance reaches 88%~92%, making it suitable for general transparent or filter materials, such as dials on instruments and radios, indicator lights on electronic displays, and light-transmitting covers for bicycle taillights. Easy to mold and process. Due to its low specific heat, low melt viscosity, strong plasticizing ability, rapid heating and molding, molding cycle is short. Furthermore, molding temperature and decomposition temperature are far apart, offering a wide range of choices. Combined with its low crystallinity and good dimensional stability, it is considered a standard processing plastic. Good coloring properties. PS surfaces are easy to color, print, and metallize, offering a wide range of dyeing options. Injection molding temperature can be lowered, allowing for use of various organic pigments with poor temperature resistance, producing bright and vibrant colors.
2.5.2 Main disadvantages of PS properties:
Its biggest disadvantage is its brittleness and susceptibility to cracking. Due to its low impact strength, it is prone to silver streaking and yielding under external forces, making material brittle and easily cracked. Parts made from it can only be used under relatively low loads. Its wear resistance is also poor; it easily scratches under moderate friction and abrasion. Its heat resistance is low. Maximum continuous use temperature of PS products is only 60-80℃, making them unsuitable for containers holding boiling water and high-heat foods. Furthermore, PS has a high coefficient of thermal expansion and poor heat resistance. Plastic products with embedded metal components such as nuts, screws, guide pillars, and spacers often develop cracks at joints. High requirements for molding and processing. Although PS is transparent and easy to mold, poor processing can lead to several problems, such as: PS products exhibit significant aging; prolonged exposure to light or storage can cause cloudiness and yellowing. PS is highly sensitive to heat and easily degrades under unfavorable heat and pressure processing environments.
2.5.3 Modification of PS
To improve shortcomings of PS, such as low strength, poor heat resistance, and brittleness, various modified forms can be prepared by copolymerizing PS with different monomers or blending it with copolymers and homopolymers. Examples include: high-impact polystyrene (HIPS), styrene-benzonitrile copolymer (SAN), etc. HIPS, in addition to possessing the advantages of polystyrene such as ease of coloring and processing, also exhibits strong toughness, impact strength, and high elasticity. SAN has high resistance to stress cracking, as well as oil resistance, heat resistance, and chemical corrosion resistance.
2.5.4 Mold Design:
PS has a significantly different coefficient of thermal expansion compared to metals. Metal inserts should not be used in PS products; otherwise, stress cracking is highly likely to occur when ambient temperature changes. Because PS is brittle and prone to cracking, wall thickness of product should be as uniform as possible, without gaps or sharp corners. Larger rounded transitions should be used at junctions of thick and thin sections to avoid stress concentration. To prevent cracking or increased internal stress due to poor demolding, in addition to selecting a reasonable draft angle, a large effective ejection area and good ejection synchronization are also necessary. PS has no special requirements for gate type, only that a large rounded transition be used at junction of gate and product to avoid damage to product during gate removal.

ABS (Acrylonitrile-Butadiene-Styrene), commonly known as super unbreakable plastic, is a high-strength modified PS, copolymerized from acrylonitrile, butadiene, and styrene in a specific ratio. Its chemical structure is as follows:

 

Ternary structure of ABS combines inherent properties of each component: Acrylonitrile provides high strength and surface hardness, improving chemical resistance and heat resistance; butadiene gives polymer some flexibility, allowing parts to possess some toughness and elasticity at low temperatures, high impact strength, and preventing brittleness; styrene maintains rigidity of molecular chains, making material hard, glossy, retaining good electrical properties and thermal fluidity, making it easy to process, mold, and dye. ABS is light ivory in color, opaque, non-toxic, and odorless, belonging to amorphous plastics. Its viscosity is moderate; its melt flowability is related to temperature and pressure, with pressure having a greater impact. ABS resin is a slow-burning material, producing a yellow flame and black smoke with a distinctive odor. It does not melt and drip while continuing to burn.
2.6.1 Main Advantages:
Good overall performance: High mechanical strength; strong impact resistance, which does not decrease rapidly at low temperatures; good notch sensitivity; good creep resistance, which does not decrease rapidly with increasing temperature; certain surface hardness, scratch resistance; good wear resistance, low coefficient of friction; Good electrical properties, less affected by changes in temperature, humidity, and frequency; Low temperature resistance down to -40℃; Resistant to acids, alkalis, salts, oils, and water;  Can be surface-decorated using methods such as painting, printing, and electroplating; Low shrinkage rate, wide range of molding processes.
2.6.2 Main Disadvantages:
Not resistant to organic solvents, will swell, and can be dissolved by polar solvents; Poor weather resistance, especially poor UV resistance; Insufficient heat resistance. Heat distortion temperature of ordinary ABS is only 95℃~98℃.
2.6.3 Modification of ABS
ABS can be blended with many other thermoplastics or polyurethanes to improve their processing and performance. For example, adding ABS to PVC can improve its impact toughness, flame retardancy, aging resistance, and cold resistance, as well as its processing properties; blending ABS with PC can improve impact strength and heat resistance; replacing acrylonitrile component in ABS with methyl methacrylate can produce MBS plastic, commonly known as transparent ABS. In summary, ABS is an ideal engineering plastic widely used in various industries. Aerospace, shipbuilding, machinery, electrical, textile, automotive, and construction industries all consider ABS as their preferred non-metallic material.
2.6.4 Mold Design
Venting: To prevent defects such as poor venting, burning, and weld lines during mold filling, venting grooves with a depth not exceeding 0.04 mm are required.

Polycarbonate (PC, commonly known as bulletproof glass adhesive) often refers to bisphenol A type polycarbonate. It boasts superior performance, exhibiting high transparency, excellent impact toughness, creep resistance, a wide operating temperature range, excellent electrical insulation and weather resistance, and is non-toxic. It is an ideal plastic with excellent engineering properties, appearing transparent and slightly yellow, rigid yet flexible. Its molecular formula is:

 

Polycarbonate has a low tendency to crystallize and lacks a precise melting point, generally considered an amorphous plastic. It has poor fluidity, cools quickly, and is prone to stress concentration in products. Its rheological properties are very close to those of a Newtonian fluid, and its viscosity is mainly affected by temperature.
Polycarbonate burns slowly, producing a yellow flame with black smoke and charcoal, melting and bubbling, emitting a distinctive fruity odor, and slowly extinguishing after being removed from flame.
2.7.1 Excellent Comprehensive Properties of PC
These are mainly reflected in following aspects:
High mechanical strength. Its impact strength is the highest among thermoplastics, even higher than aluminum and zinc, earning it nickname "plastic metal." It has a high modulus of elasticity, minimally affected by temperature; and outstanding creep resistance, exhibiting very little creep even at high temperatures and for extended periods, superior to POM. Other properties such as toughness, flexural strength, tensile strength are also superior to PA and other general plastics. PC's low-temperature mechanical strength is invaluable. Therefore, it exhibits strong low-temperature impact resistance over a wide temperature range, good cold resistance, and a low embrittlement temperature as low as -100℃.
2. Excellent heat resistance and weather resistance. PC has higher heat resistance than most plastics, with a heat distortion temperature of 135~143℃ and a long-term working temperature of 120~130℃, making it a commonly chosen plastic for heat-resistant environments. Its weather resistance is also excellent; experiments have shown that placing PC parts outdoors in environments with large temperature fluctuations, exposed to sun and rain, resulted in only slight yellowing after three years, while performance remained unchanged.
3. High molding precision and good dimensional stability. Molding shrinkage rate is basically fixed at 0.5%~0.7%, and shrinkage in flow direction is basically consistent with that in vertical direction. It exhibits high dimensional reliability over a wide operating temperature range.
2.7.2 Main disadvantages of PC:
Poor flowability; even at higher molding temperatures, flow is relatively slow. Extremely sensitive to moisture at molding temperatures; even trace amounts of moisture can cause hydrolysis, leading to discoloration, blistering, and cracking of parts. Poor fatigue resistance and abrasion resistance; sensitive to notch effects.
PC's excellent comprehensive properties make it occupy an important position in machinery, instrumentation, automotive, electrical appliances, textiles, chemicals, food industries. Finished products include: food packaging, catering utensils, safety helmets, pump impellers, surgical instruments, medical devices, high-grade insulating materials, gears, automotive lamp covers, high-temperature lenses, peephole lenses, electrical connectors, laser discs and DVDs, etc.
2.7.3 Mold Design
In addition to following general design principles for plastic products and molds, the following points should be considered when designing molds for PC products:
Due to poor fluidity of PC, dimensions of runner system and gates should be relatively large. Side gates, fan gates, and lug gates are preferred. Due to high viscosity of melt, cavity material needs to be relatively wear-resistant. Melt solidifies quickly, and flow imbalances significantly affect filling process. To prevent stagnation, cavity should achieve good filling order. PC is sensitive to notches. Product wall thickness should be uniform, sharp corners and notches should be avoided as much as possible. Corners should be rounded with a radius of not less than 1.5 mm. To prevent poor venting during molding, venting grooves with a depth of less than 0.04 mm must be created.

Polyoxymethylene (POM) is a linear polymer with no side chains, high density, and high crystallinity, possessing excellent comprehensive properties. Its most prominent characteristic is its high elastic modulus, exhibiting high hardness and rigidity.
POM is a crystalline plastic with good flowability in molten state. Its apparent viscosity is mainly affected by the shear rate, making it a shear-sensitive material.
Based on different molecular chain chemical structures, POM can be divided into homopolymers and copolymers. Homopolymers have higher density, crystallinity, and mechanical strength, while copolymers have better thermal stability, processability, acid and alkali resistance.
POM is easily flammable, with a yellow upper flame and a blue lower flame, melting and dripping, emitting a strong, pungent formaldehyde odor with a fishy smell, and continues to burn after being removed from flame.
2.8.1 Main Advantages:
POM possesses good fatigue resistance and impact strength, making it suitable for manufacturing gears subjected to cyclic loads; Good creep resistance. Compared to other plastics, POM exhibits lower creep over a wider temperature range, making it suitable for sealing parts; Good wear resistance. POM possesses self-lubricating properties and a low coefficient of friction, making it suitable for bearings and shafts; Good heat resistance. Its mechanical properties do not change significantly over long-term use at relatively high temperatures. Homopolymer POM has a working temperature of 100℃, while copolymer POM can operate at 114℃. Low water absorption; it is not sensitive to the presence of moisture during molding and processing.
2.8.2 Main Disadvantages:
Rapid solidification speed, easily leading to surface defects such as wrinkles and weld lines; High shrinkage rate, making it difficult to control dimensional accuracy; Narrow processing temperature range and poor thermal stability; even within normal processing temperature range, prolonged heating can cause polymer decomposition.
2.8.3 Mold Design
In molten state, rapid solidification, high crystallinity, large volume shrinkage necessitate a larger gate size and better flow balance to ensure proper filling and pressure holding; Good rigidity but insufficient toughness; curved gates are unsuitable for POM to prevent gate breakage and subsequent demolding failure; To prevent POM decomposition and corrosion of mold cavity, corrosion-resistant materials should be selected for cavity; POM melt has good fluidity; To prevent poor venting, weld lines, burns, and discoloration, mold requires well-designed venting grooves with a depth not exceeding 0.02 mm and a width of approximately 3 mm.

2.9.1 Relationship between Mold and Injection Molding Machine
To reduce cost of injection molding production, we want a mold to be able to operate on the smallest possible machine. Therefore, when designing mold, engineers should consider whether mold blank size can be controlled within capacity range of a smaller machine while meeting mold strength requirements.
Under normal circumstances, clamping force should not exceed 90% of rated clamping force; Rated injection volume is determined based on molten state of GPPS plastic; Normal usage injection volume (based on GPPS) range: greater than 15% of rated injection volume, less than 85% of rated injection volume; Normal usage mold dimensions: width and height dimensions given in the table minus 5mm, minimum thickness plus 5mm, maximum thickness minus 5mm.