September 1, 2022

Injection Molded Plastic Parts for Electrical Switch Holder

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This injection mold making project is an electrical switch plastic holder, the material is PC-ABS.
Electrical Switch Holder
Basic part information

  • Part size: 47.64 x 73.59 x 16.59 mm
  • Plastic material: BAYBLEND FR3010
  • Finish: VDI-18
  • Color: black
  • Production volume: 10K

Considering the electrical switch holder outer surface are visible, ACO Mold used sub gate design at the plastic holder’s edge position, sub gate have minimum gate mark left over and easy to break off during mass production, mold can be run automatically.

Basic mold information Electrical switch holder design

  • Mold type: 2-Plate
  • Gate type: Sub Gate
  • Cavity number: 1+1
  • Material: BAYBLEND FR3010
  • Shrinkage: 5/1000
  • Molding Machine (Tons): 120T

Before making the injection mold, ACO Mold did DFM and product analysis, verified some important information with customer, i.e. parting line, gate position, ejection, etc.

Electrical switch plastic holder basic mold information

After DFM process, ACO Mold start mold design.

Electrical switch plastic holder 3D design

Injection mold making took 20 days, then ACO Mold produced T1 sample parts. Considering T1 sample parts might need adjustment, ACO Mold didn’t make surface texture for T1 samples, part surface is just polished.
Electrical switch plastic holder T1 sample

ACO Mold sent T1 sample parts to customer by DHL, and got approval from the customer. Customer agreed to make surface texture, then directly start mass production of the electrical switch plastic holder, during mass production, we have a welding line problem, see pictures below, The lines across the plastic are highly visible and unacceptable by customer, the welding line is quite slim while the part surface is polish, it gets blemish look while the part surface is matt.
Injection molded electrical switch holder welding line

The reason of the welding line is simply because melt flows are spitted by steel/insert and meet on the other side, it occurs on all holes features usually, to make it as invisible as possible, the mold temperature needs to be as high as possible, so the resin melt temperature does not drop too much while it flow over the mold inserts and meet on the other side.

We also change the gate position and a sub gate to allow faster melt flow, problem was resolved at the end, take a look how we packed the parts.
Packed electrical switch holder parts

ACO Mold comments
Welding lines are a typical defects for injection molded parts with many hole features, such as computer key board typically, the hot resin flow around the little inserts and melt flow meet each other on other side where the welding line occurs, this is how welding line occurs, melt flow temperature always drop while melt resin flow over the mold cavity, that is why the welding line can only be optimized but can not be completed removed if you simply use higher mold temperature, in some other cases, changing gate position would just change the welding line to a less critical location, but for a product similar like computer key board, neither mold temperature or changing gate location would work, as a consumer product, the surface finish is quite critical thing, so as you can see now most of the key board product was painted nicely to cover the welding line defects.

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