Parting Surface: To remove finished product or solidified runner from mold cavity, mold must be divided into two or more major parts. Contact surface between these separable parts is called parting surface.

 

Figure 3-1 Definition of parting surface

Following principles should be followed when designing parting surfaces:
① Ensure required surface quality of plastic part: Parting surface should be located where it does not affect part's appearance, above product's edges, or at the ends of rounded corners. Direction and size of parting line, step difference, and fillet edge caused by parting surface must be submitted to customer for approval, as shown in Figure 3-3.

② Facilitate demolding
1. Generally, plastic part must remain on rear mold side after mold opening to facilitate ejection. Therefore, side of part with the strongest clamping force against mold should be located on rear mold side, as shown in Figure 3-4. Only in special circumstances should part be located on the front mold side.
2. Facilitate ejection. For parts with a simple outer shape and complex internal features (such as buttons and shells), outer shape should be located on the front mold side as much as possible, as shown in Figure 3-5.

 

Figure 3-5 Selection of PL surface for button plastic parts
3. When a plastic part includes a metal insert, glue area must be designed in rear mold because insert does not shrink. Furthermore, to facilitate metal insert installation, place it as close to PL surface as possible and on movable mold side.
③ Part Accuracy Must Be Guaranteed
1. Components requiring coaxiality should be molded in same mold. If molded in the front and rear molds, coaxiality will be difficult to maintain due to manufacturing and assembly errors, as shown in Figure 3-6.

 

Figure 3-6 Ensuring coaxiality
2. For box-shaped parts requiring wall thickness, to ensure uniform glue thickness, a thumbs-up design should be used between front and rear mold cores, or between front mold core and B plate, as shown in Figure 3-7.

 

Figure 3-7 Ensuring uniform glue thickness
④ Simplify mold structure.
1. Avoid side core pulls whenever possible, as shown in Figure 3-8.

 

Figure 3-8 Avoid side core pulling mechanism
If side core pulls cannot be avoided, minimize core pull distance, as shown in Figure 3-9, and design slides in the rear mold whenever possible.

 

Figure 3-9 The shorter lateral core pulling distance, the simpler and more reliable mold
2. Ensure PL surface does not interfere with normal opening of gating system. This is especially true for multi-cavity, large-gate molds with uneven PL surfaces. Parting surface at runner should not be too undulating.
3. Facilitate venting: To facilitate gas discharge, PL surface should coincide with end of material flow as much as possible, as shown in Figure 3-10.

 

Figure 3-10 Convenient exhaust
⑤ Facilitate mold processing
Ensure mold processing is as easy and cost-effective as possible. While meeting product requirements, minimize number of mold opening surfaces. Use flat surfaces (perpendicular to mold opening direction) instead of inclined surfaces, and use inclined surfaces instead of curved surfaces, as shown in Figure 3-11.

⑥ Avoid sharp corners and edges on parting surface, as shown in Figure 3-12.

If parting surface is not properly processed, sharp corners will form on mold, as shown in Figure 3-13.

 

Figure 3-13 Unreasonable parting surface
If parting surface is along normal direction of arc, sharp corners can be avoided on mold, as shown in Figure 3-14.

 

Figure 3-14 Reasonable parting surface
⑦ Meet technical specifications of molding machine.
Shortest mold opening stroke. When molded part is very deep and molding machine's mold opening stroke cannot meet requirements, a hydraulic core pulling method can be used as shown in Figure 3-15. However, increased cost of hydraulic core pulling should be considered.

 

Figure 3-15 Shortening mold opening stroke

① PL surface penetration angle should ideally be designed to be at least 3 degrees, but at least 1.5 degrees should be guaranteed. If customer's product does not meet requirements, confirmation should be sought.
② To prevent PL surface from chipping due to impact, sealing area should have sufficient area, as shown in Figure 3-16. Avoid sharp corners or lines, see Figure 3-13 for design principles of PL surface.

 

Figure 3-16 Sealing area should have enough space
③ PL surface selection order: plane, then inclined plane, then curved surface.

① Flat PL surface: If this plane is perpendicular to mold opening direction, it will directly extend to form PL surface. Note that when using UG automatic mold parting, this parting surface will have slight fluctuations at the corners (several micrometers in height), which will affect FIT mold. It should be replaced with a flat surface to facilitate grinding.

 

② Stepped PL Surface: (C: preferred with customer approval), with a pillow angle of at least 3 degrees and a minimum of 1.5 degrees.

⑧ Slanted PL Surface: Following considerations apply: a) To prevent flashing, a certain sealing distance must be left, as shown in Figure 3-17. See table below for sealing distance L. b) To facilitate processing and mold fitting, two flat locations should be left. c) To prevent slippage during mold fitting and displacement during injection, a stop or a gap (5°-10°) must be left in original body.

 

Figure 3-17 Inclined PL Surface
④ Curved PL Surface: Treatment for curved PL surfaces is the same as for inclined PL surfaces.
⑤ Compound Curved PL Surface: Parting surfaces should be treated with relatively simple smoothing. Corners should be smoothed with scanned or meshed surfaces to minimize steps and sharp corners. Direct NC machining is the criteria for determination, and EDM machining should be avoided. See PL Surface Design Principles in Figure 3-14.
⑥ Treatment Methods for PL Surfaces of Shaft Parts
1. Cut 0.1mm on both sides to create a level surface to prevent flashing that could affect shaft operation, as shown in Figure 3-18.

 

Figure 3-18 Axis CUT0.1
2. Front and rear molds must be aligned and closed to prevent misalignment that could affect shaft operation, as shown in Figure 3-19.

 

Figure 3-19 Mold closing process
⑦ Treatment of front PL surface against punch hole:

⑧ Treatment of side piercing hole:
In principle, penetration slope should be at least 3 degrees, and under restricted circumstances, at least 1.5 degrees, as shown in Figure 3-20.

 

Figure 3-20 Side puncture
⑨ Treatment of upper and lower piercing surfaces: Whenever possible, use a punch hole instead of a punch hole, as shown in Figure 3-21. Ensure punch hole slope is at least 3 degrees and at least 1.5 degrees (height difference must be at least 0.2).

 

Figure 3-21 Processing of upper and lower intersecting surfaces
⑩ Selection of PL surface at buckle: As shown in Figure 3-22, PL position in left figure is unreasonable, resulting in flash at buckle, making it difficult to guarantee correct dimensions and affecting product's functionality. If PL is adjusted to position shown in the right figure, even if flash occurs, no correction is required as it will not affect product's functionality.

 

Figure 3-22 Selection of PL surface at buckle
⑪ Treatment of PL surface step difference and direction: 1. Amount and direction of PL step difference that affect appearance, function, and dimensions must be confirmed by customer. 2. Design data correction amount should be 0.02 to 0.1mm depending on part size. 3. Factors for selecting two step difference methods shown in Figures 3-23 (a) and (b): Visual direction of product's exterior surface, paper feed direction, rotation and sliding directions, contact surface with people during handling or use, and location of PL surface (generally, large surfaces should avoid sharp corners).

 

Figure 3-23 Processing of PL surface step difference and step difference direction
⑫ Treatment of pillow position:
1. Tilt, treatment method, and PL position of pillow position must be confirmed by customer before implementation.
2. Treatment methods are as follows:
a. Reduce the glue to create a step difference, as shown in Figure 3-24; pillow position tilt 3° or more, at least 1.5° (height difference must be at least 0.2). See table below for sealing distance L.

 

Figure 3-24: Stepping with Reduced Glue

b. Build a horizontal position, as shown in Figure 3-25. Pillow position should have a slope of at least 3° and a minimum of 1.5° (height difference must be at least 0.2).

 

Figure 3-25: Walking position at pillow position
c. Partially eliminate R angle, as shown in Figure 3-26 (not recommended). Refer to 05-T1-103. Pillow position should have a slope of at least 3° and a minimum of 1.5° (height difference must be at least 0.2).

 

Figure 3-26 Cancellation of R angle at pillow position