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The Solution of Injection Filling Problem of Injection Mould

We recently did a project for a Lithuania customer. This product is a set of lid-housing plastic case, the parts worked as outer protection shell of electronic products, it is made in PC which is well know as the hesitation of melt flow, part design has quite many ribs features as well as heavy over all wall thickness, the injection filling have been a challenge to our team. Below is the experience sharing of this project:

Basic part information:
  • Part size: 81.94X163.79X36.70 mm 
  • Part size: 82.00X163.85X22.00 mm
  • Plastic material: PC 
  • Finish: YA1286A 
  • Color: Ral 9011 
  • Production volume: 2 K
Firstly, we do the analysis of DFM
Analysis of DFM

Consideration of usage and cost of the product, we go with mold layout 1+1.

Basic mold information´╝Ü
  • Mold type: 2-Plate 
  • Gate type: Side Gate 
  • Cavity number: 1+1
  • Material: PC 
  • Shrinkage: 6/1000
  • Molding Machine (Tons): 160T
Considering the difficulty of the filling, we plan to do a big edge gate at first, that would be easier for us to full fill the cavity during injection moulding, but the edge gate will leave a ugly and obvious gate mark on side surface, the client wants the out surface looking good. So we have to change the gating method to sub-on-pin gate, an extension feature are created to make a channel so the melt flow can go into mould cavity from a non-critical surface, see below the sub gate, actually this is quite risk to do so, as the part over all wall thickness is quite heavy, this little gate is very difficult to full fill the part, but the client just insist on it.
Gate Type1



Gate Type2
Gate Type1
 Gate Type2

After confirming, we did the 3 D design of mould, as pictures below:
3D Design of Mould

After the customer confirmed the 3 D mould,we began to produce the mould, and the delivery time is 4 weeks. We updated and reported the progress weekly
Rough/Finish machining of mould, as pictures below:
Rough or Finish Machining of Mould
Rough or Finish Machining of Mould2
Rough or Finish Machining of Mould3

 Electric sparking machining, and texturing of surface of mould and the final mould fitting, as pictures below:
           Injection Mould Parts Sink MarksInjection Mould Parts Sink Marks
Injection MouldInjection Mould
 We did the T 1 sampling of mould on time, but T1 sample's result is not ideal. The part is very difficult to be full filled, we have to use very high injection pressure to fill it as much as we can, but still sink marks are all over the part, also due to high injection pressure and rough surface texture, the part stick to cavity side strongly, we can not go on without adjustment. 
T1 Sampling of MouldT1 Sampling of Mould

After T 1 sampling, we did some changes by adding some under-cut and textures one the back side of the product to avoid the sticking problem. Below is the pictures of sample we made at T2, we also enlarge the gate point as much as possible to ease the filling problem.
T2 Sampling of Mould

We did red color for mass production.
Red Color ProductsRed Color Products
Red Color Products3

Tips:

  • PC resin is a transparent, hard material, it was frequently adopted in medical, packing, lighting, electronic industrial,  injection moulding for PC material is proved to be tricky sometimes because this resin has bad melt flow property, it is also easy to get surface blemish and filling problem. 
  • Usually it requires bigger edge gate so ease the melt flow hesitation, the runner has to be S or L shape to avoid direct melt flow pouring, small sub gate/small point gate was proved to be problematic, ideal wall thickness 2.5-3mm, better to do mould flow analysis if the part structure is complex. 


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