Power tool housing injection mold design

Time:2019-12-31 17:59:24 / Popularity: / Source:

1. Introduction

In this paper, injection mold design of power tool casing is taken as an example to introduce design features of plastic injection mold tooling exported to Netherlands. Netherlands is a constitutional monarchy, located in northwest of Europe, European origin of famous Eurasian Continental Bridge. Europe is one of the most developed regions in the world for mold industry. Germany established its own mold standard system in 1950s. The most commonly used European injection molds standard are German HASCO standard.
German STRACK standard, German EOC standard, British DMS standard, US DME European standard (metric standard), French ROUBARDIN standard and Austrian MEUSBURGER standard, the most famous of which is German HASCO standard. European molds have advantages of high efficiency, precision and long life. The most important factor in determining mold reliability is injection mold design and mold maintenance, but also mold steel, heat treatment methods and mold processing. A set of high-quality molds should fully understand and meet needs of customers, be tailor-made solutions for different products of different customers in line with customer's philosophy. Dutch mold industry is developed. St. Wanhao, world's leading hot runner supplier for automotive industry, was born in the Netherlands.
plastic injection mold tooling 
plastic injection mold tooling 
Figure 1 Power tool housing product drawing
Basic requirement of injection molds for Dutch customers is that molds generally follow HASCO standard. Steel used meets requirements of MOULD SPECIFICATION. Mold ejection system adopts European strong pull-up form. Nozzle material and products can be automatically separated in mold, no need to manually remove runner, and injection molding can be fully automatic.

2. Product analysis

Power tool housing product diagram is shown in Figure 1. Product has force and torque requirements during use. Therefore, material is PA+30%GF. Material is nylon plus 30% glass fiber material. The higher glass fiber content, the higher hardness of material, the lower plasticity, and the smaller shrinkage rate. Glass fiber also has an anisotropic effect. Shrinkage rate is different in the direction perpendicular to flow direction and parallel to flow direction. This set of molds has obtained consent of guests, and shrinkage rate is 0.5%. Nylon material has excellent fluidity, but it is easy to produce a frontal edge. After adding glass fiber material, fluidity of material does not decrease, and glass fiber is easy to wear on mold cavity. Therefore, mold for molding glass fiber material needs to improve processing precision, so that mold clamping portion is not easy to generate a frontal edge. Another important point of injection molding glass materials is need to properly increase temperature of injection molding machine barrel to avoid floating fibers on the surface of plastic part. Molds exported to Europe are available in 2D and 3D formats. 3D drawings are used for 3D parting, which facilitates CNC machining and electrode design. 2D drawings mark dimensional tolerances and technical requirements, volume of plastic parts, average glue position thickness, appearance requirements and color. Information such as interchangeable inserts are included in 2D product drawing, and information on 2D surface is also basis for dimensional inspection report after mold trial. Technical requirements of power tool casing are shown in Figure 2. Dimensions of small rounded corners of plastic parts are shown in 3D drawing. Average glue position thickness is 2mm and volume is 29.8cm3. Dimensional tolerance of plastic parts should conform to German national standard DIN 16901. Main non-sunning surface draft angle is 1°, main embossed surface draft angle is 2°, and remaining un-surface surface draft angle is 0.5°.Except for boundary of parting surface, unmarked edge rounding is R0.2.
injection mold design 
Figure 2 Power tool housing technical requirements
Draft of all surfaces is reduced and drafting direction is shown in Figure 2. For design of export molds, it is usually customary to reduce size of mold, but direction of draft should be noted. For special parting parts, it should be presented to guests at opening meeting, an results of negotiation will be recorded in injection mold design SPECIFICATION to avoid future disputes.
Three elements of export plastic injection mold design are: runner gate form, ejection mode and thimble arrangement, and parting surface. These three elements have actually completely determined mold structure. In mold matching meeting, determination results of three elements are recorded in mold design style book. Parting surface of product is shown in Figure 3. Thimble on moving mold side of product should be lower than surface 0.15mm, flaring surface of parting surface is less than 0.2mm, and appearance requirements are in accordance with sample.

3. Injection mold design points

Design of power tool shell mold is shown in Figure 3. According to size and structural characteristics of product, mold adopts design of 2 cavity, and feeding method is that diving port is glued on the side of product, as shown in Fig. 4. It can be automatically separated when mold is opened. Large slider cores are designed on both sides of product. As shown in Figure 5, slider is driven by a slanted guide column, and wear plate is designed on both slope and bottom of slide. It is made of oil steel, oil groove and heat treated to HRC58.
Oblique guide column drives lateral core pulling mechanism widely used in European and American export molds. If oblique guide column drives lateral core pulling mechanism to meet design requirements, it must be driven by inclined guide column instead of other structures, because inclined guide column drive has advantages of stable operation, safety and reliability, and easy manufacture.
Ejection of product adopts dome needle to eject, and injection molding machine pushes out ejector plate, adopting strong pull-up shape commonly used in Europe. That is, ejection and return of ejector plate are all made by pull rod, and ejector plate is pulled back by ejection and returning action of injection molding machine. Feature of this ejection mode is that ejection and return position are reliable and accurate, and injection molding cycle is effectively reduced. When designing a strong pull, it must be noted that spring cannot be placed over return needle, otherwise ejector plate will be deformed by force. Ejector design is shown in Figure 4.
Return position of ejector plate must be accurate and reliable, and die ejector plate is designed with a stroke switch. Front and rear molds are made of German steel 1.2344 and heat treated to HRC48~52, which effectively slows abrasion of glass cavity.
In Dutch mold, lock module 13 has a large design size. At the same time of clamping mold, it also functions as a hanging mold. LIFTING BAR is painted with red paint, and fixing bolt is raised above surface of hanging beam. Purpose of red paint is to remind operator to remove hanging beam before injection molding.
injection mold design 
Figure 3 Power tool housing injection mold design
injection mold design 
Figure 3 Power tool housing injection mold design (continued)
injection mold design 
Figure 4 Schematic diagram of gate
In European molds, bottom of thimble plate is usually not used as a garbage nail, a garbage tank is opened, or neither a garbage nail nor a garbage tank is provided. This set of molds belongs to the latter.
Small parts of front and rear molds are designed with inserts for easy processing and exhaust. Front and rear molds are shown in Figure 6 and Figure 7. Technical requirements for injection mold design and manufacturing are generally indicated on mold drawing, as shown in Figure 8.
injection mold design 
Figure 5 slider design
injection mold design 
Figure 6 Front mold
injection mold design 
Figure 7 Back mold

4. Conclusion

Design of export mold must conform to customer's design philosophy. Customers in different regions of world have different ideas about injection molds, which are determined by different cultural concepts. Design of export mold needs to be familiar with customer's mold standard and strictly in accordance with customer's MOULD SPECIFICATION. Focus on size inspection and strict processing according to drawings of mold parts, to eliminate traditional backward process such as artificial matching. We must continue to learn advanced European technology and management concepts, and strive to improve core strengths and competitiveness of company itself.

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