Looking at design concept of French molds from a set of small molds

Time:2020-10-31 11:53:06 / Popularity: / Source:

1 Introduction

France is an industrially developed European country. Europe is one of the most developed regions in the world for mold industry. French standard for injection molds is ROUBARDIN standard, and famous German HASCO standard is also adopted in France. European molds have advantages of high efficiency, precision and long life. At the same time, the most important factors that determine mold reliability are mold design and mold maintenance, as well as mold steel, heat treatment methods, and mold processing technology. A set of high-quality molds should fully understand and meet needs of customers and be in line with customer concepts, tailor-made solutions for different customers' different products.
Different cultural concepts determine different mold structures. Concept of export molds is that molds designed must conform to design concepts of customers.
Customer satisfaction is the only criterion for judging qualification of molds. We must produce high-quality molds that are satisfied and desired by customers. Concept of quality, including appearance of mold, makes customers think that mold is tailor-made for them and is carefully crafted. Conditional large-scale export mold factories need to categorize and manage customers. Different customers have different requirements and develop different mold manufacturing process standards for customers to meet their needs. It is necessary to communicate with customers in advance, obtain consent for production of real materials and substitute materials.
Cost concept is to meet requirements of reduction of strength without being fat and big ears, resulting in waste of steel and production efficiency of injection molding. Choose appropriate mold standard parts that meet customer needs.
Accuracy of data, including mold design drawings, mold instructions, material certificates, heat treatment certificates, sample quality reports, packing lists, etc., are all very important. In the era of big data, machine tools, equipment, advanced materials, tools, and advanced software can all be purchased with money, while big data cannot be bought, or the ones bought are not suitable for you.

2. Product analysis

Plastic part is a plastic bearing outer ring, see figure 1, material is Delrin 100 NC-10 natur, this material is a kind of POM, commonly known as Trane, it is a kind of high crystalline polymer, with a smooth surface, shiny, small water absorption, stable size, wear resistance, high strength, good self-lubricity, good coloring, oil resistance and peroxide resistance. POM has better comprehensive properties, is the hardest among thermoplastics, and is one of plastic materials whose mechanical properties are closest to metal.
1. Its tensile strength, bending strength, fatigue resistance, abrasion resistance and electrical properties are very good, and it can be used for a long time between -40℃ and -100℃. Trane makes a wide range of gears, bearings and other parts, can also produce high-end small household appliances shells, such as high-end electric toothbrush shells.
Size of plastic part is small, and structure is very simple. Mold structure diagram is shown in Figure 2.
mold design and manufacturing 
Figure 1 Product drawing of bearing outer ring

3. Key points of mold design

3.1 Automatic separation of nozzle

French mold is characterized by automatic molding. It can be injected in hot nozzles, or by diving and banana (horns). All nozzles must be automatically cut off and fall automatically. According to size and structural characteristics of product, this set of molds adopts a design of 1 out of 8. Feeding method is to feed on the side of product at diving port, align with 5 mold design drawing (continued), and it can be automatically separated when mold is opened. All molds avoid general large nozzle injection, and rely on manual post-processing to cut nozzle to realize separation of nozzle and product. First, because of high labor cost, manual post-processing and cutting of nozzle is very different, manual cutting of nozzle requires a water-mouth pliers or knives. Plastic parts are easily scratched and cause defects, people are also easily injured and fatigued. Therefore, manual cutting of nozzle material does not conform to customer's concept.
mold design and manufacturing 
Figure 2 Mold design drawing

3.2 Sprue sleeve form

Two ends of sprue sleeve of European molds are usually flat, which is different from domestic spherical surface, while two ends of sprue sleeve of French mold are also flat, but gate is a 120° inverted cone. This is because precision of injection molding machine is different, and nozzle end structure of injection molding machine is also different. Figure 3 shows structure of sprue sleeve 3. For more structure, please refer to ROUBARDIN standard.

3.3 Temperature control system design

In the cycle of thermoplastic injection molding, cooling time of mold accounts for more than 80% of entire cycle. Effective cooling circuit design can reduce cooling time, thereby increasing total production. In addition, uniform cooling can reduce residual stress caused by uneven heat transfer, thereby controlling warpage of finished product, so as to maintain accuracy and stability of molded product size, and improve quality of product. French mold regards entire mold as an independent temperature control system. In order to reduce displacement of injection molding machine, a heat shield 2 and a heat shield 18 are respectively designed on panel 1 and chassis 17, and panel 1 is also designed with a cooling circuit, see Figure 5. Good water transportation design effectively reduces injection cycle. Water connector generally adopts Staubli brand.
mold design and manufacturing 
Figure 3 French mold sprue sleeve
thermoplastic injection molding 
Figure 4 Mould design drawing (continued)

3.4 Exhaust design

This set of molds has no inserts, cavity is directly made on A plate 6, and core is directly made on B plate 8. POM plastic has strength, so A plate 6 and B plate 8 are made of S136 and heat treated HRC48-52. During injection process, air in mold cavity (cavity) must be smoothly discharged so that plastic can be filled smoothly. When exhaust is poor, surface of product (workpiece) will have bubbles caused by trapped air, and even burn marks. Exhaust system design is shown in Figure 4 and Figure 7. Importance of exhaust system design has been paid attention to by mold manufacturers. However, many domestic mold manufacturers have not standardized exhaust design and production. Although some manufacturers do exhaust, exhaust is to be supplemented by mold fitter according to sample situation after mold trial. In this way, production of exhaust is completely done with personal experience of mold master, there is a lot of blindness, and exhaust data is not reflected on the surface of mold drawing, which is completely unfavorable for accumulation of data, inheritance and summary of experience. For molds exported to France, exhaust must be designed in advance on the surface of mold drawing, and exhaust manufacturing is also processed in accordance with drawings. In many cases, determination of mold exhaust position needs to be judged according to results of mold flow analysis. Other technical requirements for mold design and manufacturing should also be marked on mold drawing. Therefore, to design export molds, a 2D drawing of mold structure is necessary. It reflects concept of mold design and is not optional.
thermoplastic injection molding 
Figure 5 Mold design drawing (continued)

3.5 Guiding and positioning system design

Overall mold design uses design features of European mold bases, that is, mold base guide pillars 3 large and 1 small, plate thickness and mold plate end band 6, guide pillars are positioned between all mold plates, front mold of guide pillar is inserted into rear mold guide sleeve. A positioning ring 4 and 16 are respectively designed for front mold panel and rear mold panel, which are characteristics of European molds.
There is a gap between mold guide post and guide sleeve, so mold must be designed with a precision positioning block 20. All three sets of precision positioning are designed in the middle of mold plate to reduce error after thermal expansion.
For guiding of ejector plate, ejector plate guide post 19 and ball guide sleeve 12 are designed. There is a 3mm gap between top of ejector plate guide post 19 and B plate. Ejector plate with this design has higher precision. Mold does not have a needle back. Product is ejected by a barrel ejection, while nozzle material is ejected with an alignment needle. Ejection of ejector plate by injection molding machine adopts strong tensile ejection method commonly used in Europe, that is, ejection and return of ejector plate adopt pull rod. Through ejection and return action of injection molding machine, ejector plate is pulled back. Characteristics of this ejection method are that ejection and return are reliable, accurate, which effectively reduces injection molding cycle and facilitates automatic injection molding.
When designing a strong top, it must be noted that there should be no back stitches on mold base, or no springs can be placed on back stitches, otherwise ejector plate will be deformed by force.
thermoplastic injection molding 
Figure 6 Mold design drawing (continued)

3.6 Trash nails

In European molds, bottom of thimble plate is usually not made of garbage nails and put in garbage chute. For small molds or neither garbage nails nor garbage chute, this set of molds belongs to another part.

3.7 Hanging form beam design

Lifting of export mold is very important. As shown in Figure 6, hanging mold beam is specially designed, center of gravity position is calculated, and lifting bolt hole is designed. Hanging mold beam needs to be painted with red paint to remind operator that it must be removed from injection molding machine before operation.

4 Conclusion

Many domestic practitioners have the least contact with exported molds and confuse molds exported to Europe and United States. In fact, European and American molds are replaced by similar places and cannot be collectively referred to as European and American molds. Design of export mold must conform to customer's design philosophy. Customers in different regions of world have different ideas for injection molds, which are determined by different cultural concepts. Design of export molds needs to be familiar with customer's mold standards and strictly follow customer's mold specifications design. Dimension inspection, processing strictly in accordance with drawings of mold parts, eliminating traditional backward technology such as manual matching. We must continue to learn European advanced technology and management concepts, strive to improve our own core advantages and competitiveness.
thermoplastic injection molding 
Figure 7 A plate and its exhaust groove

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