Mold Making is an important step in product development. Car Dashboard mold design case study to understand how to conduct mold design.
The car dashboard photo is shown below. The overall dimension of the product is 343.40 mm x 167.13 mm x 48.01 mm, the average thickness of the plastic part is 2.00 mm, the material of the plastic part is PP TD40, the shrinkage rate is 1.010, and the quality of the plastic part is 208.88 grams. The technical requirements for plastic parts are that there must be no defects such as peaks, unfulfilled injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, etc.
This is the internal bracket of the dashboard of a Japanese car. As can be seen from the photo above, the mechanical design of the plastic part is a flat complex shell, the dynamic and fixed mold has many bone positions and column positions, the size is large, and the mold is a large mold. The plastic part is made of PP td40. Calcium carbonate filler is added to the material, mainly to increase the rigidity and fatigue resistance of the plastic part and play the role of shock absorption.
Due to the large size of plastic parts, the cavity ranking of mold design is 1 out of 1, the injection molding machine is 220 tons.
Mold design stylebook is an important document of mold design. It stipulates the number of cavities, the way of plastic injection, the brand grade of mold core steel and standard parts, mold life, model of the injection molding machine, and injection cycle, which are the basis of mold design.
Here are the most common terms of molds:
Mold review meeting; Mold unloading inclined portion; Mold locking force; T0 sample; Dimension; Gate sleeve spherical surface;
The mold review meeting is to review the problem points and improvement countermeasures of product and mold mechanical design and determine the parting surface, ejection mode, and gate of the mold. All review contents shall be marked in the product drawing and written in the mold stylebook with red and blue pencil or pencil. After the review, fill in the relevant review records, seal on the drawings, and sign for confirmation by both parties.
The Importance of Mold Design Positioning Systems
The guide pin and sleeve of the mold are the primary positionings of the entire mold. Because there is a gap of 0.01-0.03mm between the guide pin and the hole of the guide sleeve, it is obviously not enough to rely only on the guide pin and guide sleeve for positioning large molds. Four conical positioning parts are designed on the four sides of the mold block. The three-level positioning refers to the precise positioning of the design tiger mouth on the mold core, which mainly protects the accurate positioning of the inserting surface of the mold.
Two three-level positioning systems are designed for the mold of the car dashboard. The first is to design the tiger mouth positioning around the guide pin and guide sleeve of the mold block. The second is to design the tiger mouth positioning at the four corners of the front and rear of the mold core. The design of so many positioning mainly takes into account that the car dashboard mold belongs to a large mold and has the design configuration of mold core eccentricity. Therefore, it is very important to design effective positioning and guidance. In order to balance the mold locking force, a balance weight is designed on the parting surface.
The exhausting slot of a large injection mold is very important. The way of exhausting-slot must be analyzed in advance, focusing on the areas easy to trap gas, and the exhaust must be designed on the mold drawing. An exhaust shall also be ground at the edge of the insert to facilitate injection mold filling.
Car Dashboard Mold Design Highlight
Due to the large size of the plastic part, the cavity is arranged one out and one eccentrically. The mold block is the standard mold block CH5565. The front and rear of the mold cores are positioned and locked by extrusion blocks. Positioning pins are added between the B plate of the moving mold, square iron, and bottom plate to maintain the rigidity of the mold.
The area of plastic parts is large and the molten plastic process is long, so the design of the gating system is very essential. Considering that there are many bones and holes in plastic parts, there are many factors affecting the flow of molten plastic and large filling resistance. Therefore, the gating system is designed with a 3-point latent gate, which is located on the same side of the plastic part. The runner pull pin is designed with a tapered pull pin to facilitate the manipulator to grasp the material at the water intake.
The ejector system of plastic parts adopts an ejector pin and cylinder ejector. In order to make the ejection system smooth, some innovative designs have been made. The middle support guide pin is designed, which is guided by graphite middle support. The top of the middle support guide pin is fixed on the back of plate B with locating pins, and the bottom is fixed on the moving mold plate with screws. The design of the middle support guide pin has the best guiding performance and overcomes the disadvantage of the poor verticality between the traditional middle support guide pin and the thimble plate.
At the same time, the middle support guide pin can also act as a support head. For the convenience of mold installation, M10 threaded holes are designed on the end face of the return needle to tighten the thimble plate. At the same time, limit screws are designed on the thimble plate, and positioning pins are designed on the top of the support heads. All thimbles adopt Japanese Misumi high-speed steel thimble SKH51.
The cooling system design of the mold is shown below. The front and rear molds are designed with direct water transportation and ponds to effectively ensure the cooling effect.
The total type of mold parts is more than 40 and the number is nearly 100, so the reasonable identification of parts is particularly important for design and production.
Firstly, according to the role of each part in the mold, the parts can be divided into four categories: template, cavity, mechanical parts, and standard parts. The template constitutes the matrix of the mold, the cavity is the core of the mold, and the mechanical parts and standard parts are the auxiliaries of the mold.
Here are numbers and details of parts specified in the mold drawings:
How To Manage Parts Design In 3D Drawings
The drawing number of parts is prepared on this basis and expressed by 3 Arabic numerals. After determining the part drawing number coding rules, similar parts can be set in different layers during 3D parting. The drawing numbers are arranged clockwise or counterclockwise on the assembly drawing:
1) The formwork is arranged in M1, M2, M3… Order from the fixing plate of the fixed mold to the fixing plate of the dynamic mold;
2) Cavity parts (fixed mold) are arranged in the order of V1, V2, V3;
3) Core parts (dynamic mold) are arranged in the order of C1, C2, C3;
4) Sliding block parts are arranged in sequence of S1, S2, S3;
5) Inclined roof parts are arranged in order of L1, L2, L3;
6) The auxiliary parts of the fixed mold are arranged in the order of A1, A2, A3;
7) The auxiliary parts of the dynamic mold are arranged in the order of B1, B2, B3;
The specific meaning of the part number is: the first letter indicates the category of parts, and the following number is the sequence number of parts. This classification drawing number is simple to write and can achieve the purpose of classified management and classified processing of parts. In the specific mold design, it is necessary to ensure that the part drawing numbers of 2D and 3D drawings of the mold are consistent, and the drawings are consistent with the physical mold parts and even write on the mold parts when necessary, so as to facilitate the maintenance and replacement of the mold parts in the future.
When the mold is changed, the number of parts will change. For modified parts, add A, B, C, D… After the drawing number to indicate different versions. For new parts, write a new drawing number according to the rules. For all newly added and modified drawings, the drawing date on the drawings shall be updated to facilitate the production management.