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Can my model be injection molded? Take a look

Question asked by Liam Ellis on May 28, 2011
Latest reply on Aug 3, 2017 by Silikon Technologies

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I am in my second year at university (BE Mechatronics) and we have been set an assignment to model a casing for a surface mount printed circuit board. We are expected to design the mold for the part so it can be inction molded (We will not physically create any parts however). I have no experience in design with regards to injection molding / flow design etc and before I go ahead and create my mold etc I am hoping someone can have a brief look at one of my parts (Attached below) to suggest any crucial changes or flaws that my design would encounter during the injection process.

Please ignore the lack of filleting on some edges, these will be filleted later when all geometry has been checked. I am really just looking fo any pointers with regards to the layout / general design. Also which direction would be suitable for the plastic to enter the mold?

I really have little idea about this process so any information would be greatly appreciated

Best regards

Liam

The 'Top' file attached is my piece in question, the other file is an assembly drawing

Deepak Gupta May 29, 2011 6:48 AM

Correct Answer

Welcome to SW forums Liam

Yes the part can be injection molded but you need to do some more action on the part. I'm not a regular injection molding guy so expect more suggestions coming in:

1 The part doesn't have proper drafts which is a very important factor for plastic parts. This article should help you to understand more on it: http://www.paralleldesign.com/moldability_101/draftangles.htm You can run the draft analysis from View > Draft Analysis and then add the proper draft to you parts.

2 Try to maintain a uniform wall thickness wherever possible. as this will help in proper filling of the area while injection molding.

3 Do a search over Internet or refer some books to understand more on plastic part designing. You will find these articles helpful:

http://www.xcentricmold.com/design_guidelines.html

http://www.brighthub.com/engineering/mechanical/articles/45260.aspx

http://www.shapedesign.biz/plastic_part_guide_tips.html

http://www.chplastics.com/chblog/5-tips-for-quality-plastic-part-design/

You might also find this post helpful for your future reference.

See the reply in context

Attachments

Assem1.SLDASM.zip420.9 KB
Top.SLDPRT.zip405.9 KB

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Deepak Gupta May 29, 2011 6:48 AM

Welcome to SW forums Liam

Yes the part can be injection molded but you need to do some more action on the part. I'm not a regular injection molding guy so expect more suggestions coming in:

2 Try to maintain a uniform wall thickness wherever possible. as this will help in proper filling of the area while injection molding.

3 Do a search over Internet or refer some books to understand more on plastic part designing. You will find these articles helpful:

http://www.xcentricmold.com/design_guidelines.html

http://www.brighthub.com/engineering/mechanical/articles/45260.aspx

http://www.shapedesign.biz/plastic_part_guide_tips.html

http://www.chplastics.com/chblog/5-tips-for-quality-plastic-part-design/

You might also find this post helpful for your future reference.

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Liam Ellis @ Deepak Gupta on May 29, 2011 5:36 AM

Hey thank you so much this is exactly the kind of info I want! I look forward to any other suggestions

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Matt Lombard May 29, 2011 11:21 AM

There's no draft, and while it may be technically possible to mold some things without draft, this one would be difficult because of the thickness of the walls. On a 4" part, you would not normally see walls that are 0.3" thick. Something in the 0.06" - 0.15" would be more likely, depending on the usage of the part. Another suggestion would be with the fillets. Where you have holes that go through the part, the parts are usually designed with fillets on only one side. Putting fillets on both the inside and outside ends of a hole mean that you have to have steel protruding from both the cavity and the core sides, and they have to meet exactly in the middle. If you only have fillets on one side, the steel from one side can go all the way through and touch against a big flat face on the other side.

I'm no mold builder, but I'm a plastic part designer with a bit of experience talking with mold designers and builders. I remember being in your position, where I didn't know what could be done, and it was all new. If you plan to do more plastic part design, there is a lot out there to learn, and most of it can't be learned in books. It's challenging stuff, and there's a lot to learn. Have fun with it.

Actions

Liam Ellis @ Matt Lombard on May 30, 2011 8:50 PM

Hey thanks Matt, another useful suggestion I'd never considered. Ive got enough information now to get a mouldable part model put together based on the expectations of the assignment. Cheers for the quick and helpful response.

Actions

Ryan Laplante @ Liam Ellis on Mar 14, 2012 5:02 PM

I am modifying or rebuilding the basic geometry of a countertop soda machine to be molded from plastic and this forum, the provided links and the info contined within is priceless.

Actions

Josh Wood Mar 4, 2013 1:24 AM

Yes your model can easily be the injection molded. You can procced with it. Good luck.

_______________

micro molding

Actions

Ant Arg Mar 5, 2013 2:01 AM

This part can be injection molded but it it is going to be very hard to manufacture the tooling for it. Not sure what material you are going to use but most likely polyprop. Always make a seperate configuration with your shrinkage added. That way you use the one config for you product drawings. And the other config for your mould design. NEVER forget your shrinkage. It is the dumbest mistake and you will have to tell your boss how dumb you are and everyone will laugh at you. I have created a macro that adds shrinkage and creates a seperate configuration.

Those 3mm slots will have to become 3mm cores shutting off against the cavity. That means a 3mm end mill cutter. Not gonna be easy. Unless you spark erode which is 0.2mm spark gap Which leaves you 1.1 mm and you will have to polish by hand. Not an option.

Draft analysis tool will throw you off. If you can even get it to work properly. Solidworks split line tool is also difficult to work with and its just easier to do it all by your self that way you know its correct. Last thing you want is the mould coming back full of flashing because solidworks thought everything was going to shut off niceley but it didn't.

I have used a 0.2 degree taper of injection moulded parts and its worked fine.

And you wil only need the taper on your core. Not the cavity. Remember the shrinkage makes the part stick to the core. However it is good practice to put shrinkage on your cavity.

The radii will be formed with the ball nose cutter that is used on the cnc machine. So if you want a 1mm radius then the toolmaker will use a 2 mm ball nose cutter. Bit small, rather go for a 4 or a 6. You will not notice the difference on the end product.

Those circular holes will be formed by drilling through the core and putting pins throught the holes. So getting a radius on them will be difficult. Remove the radii. It will save you a lot of trouble.

Unfortunately you learn the most form the mistakes you make. Injection moulds can be expensive. Sometimes very. And the mistakes will just add to that cost.

What i recommend... Contact a mould manufactureing plant in china. Send them the product. Get them to make you a mould for next to nothing. Let them worry about all of this. You can afford to fly there and inspect the mould for what they charge. We have had moulds delivered in 30 days for peanuts. LITERALLY.

Actions

Katie Maurer @ Ant Arg on Dec 2, 2015 7:59 AM

Hey thanks Ant, your idea may be very easily to mould the tools with injection moulding..but another suggestions is with the help of art injection moulding are semi or fully automated with pick and place robots..

Actions

David Sloop @ Ant Arg on Dec 2, 2015 9:01 AM

"Contact a mould manufactureing plant in china"

What? Why???

That kind of mentality is why many people (me included) had to re-invent ourselves for a career outside the plastics industry.

I had a good ten years out of college designing plastic parts and molds, until cheap Chinese molding drew all the molding and mold building out of the US.

Fortunately, companies found they often get what they pay for, and some of the business is coming back. Some mold shops have made a shift in service by specializing in repairing Chinese molds that wore out too quickly, or didn't produce quality parts.

It doesn't sound like the OP is planning a career in plastics, but if he was, I'd recommend contacting a local molder, or mold builder, and picking their brain. Make a contact in the industry, and learn something.

Actions

Silikon Technologies Aug 3, 2017 5:34 AM

Hello guys

With the years of experience in precision we manufacture silicon injection molding products that help saving our customer’s time & money. Click here to know more!

Medical Silicone Molding

Actions

10 Replies

Deepak Gupta May 29, 2011 6:48 AM
Unmark Correct
Correct Answer
Welcome to SW forums Liam

Yes the part can be injection molded but you need to do some more action on the part. I'm not a regular injection molding guy so expect more suggestions coming in:

1 The part doesn't have proper drafts which is a very important factor for plastic parts. This article should help you to understand more on it: http://www.paralleldesign.com/moldability_101/draftangles.htm You can run the draft analysis from View > Draft Analysis and then add the proper draft to you parts.

2 Try to maintain a uniform wall thickness wherever possible. as this will help in proper filling of the area while injection molding.

3 Do a search over Internet or refer some books to understand more on plastic part designing. You will find these articles helpful:

http://www.xcentricmold.com/design_guidelines.html

http://www.brighthub.com/engineering/mechanical/articles/45260.aspx

http://www.shapedesign.biz/plastic_part_guide_tips.html

http://www.chplastics.com/chblog/5-tips-for-quality-plastic-part-design/

You might also find this post helpful for your future reference.
Like • Show 0 Likes0
Actions
- Liam Ellis @ Deepak Gupta on May 29, 2011 5:36 AM
  Mark Correct
  Correct Answer
  Hey thank you so much this is exactly the kind of info I want! I look forward to any other suggestions
  Like • Show 0 Likes0
  Actions
Matt Lombard May 29, 2011 11:21 AM
Mark Correct
Correct Answer
There's no draft, and while it may be technically possible to mold some things without draft, this one would be difficult because of the thickness of the walls. On a 4" part, you would not normally see walls that are 0.3" thick. Something in the 0.06" - 0.15" would be more likely, depending on the usage of the part. Another suggestion would be with the fillets. Where you have holes that go through the part, the parts are usually designed with fillets on only one side. Putting fillets on both the inside and outside ends of a hole mean that you have to have steel protruding from both the cavity and the core sides, and they have to meet exactly in the middle. If you only have fillets on one side, the steel from one side can go all the way through and touch against a big flat face on the other side.

I'm no mold builder, but I'm a plastic part designer with a bit of experience talking with mold designers and builders. I remember being in your position, where I didn't know what could be done, and it was all new. If you plan to do more plastic part design, there is a lot out there to learn, and most of it can't be learned in books. It's challenging stuff, and there's a lot to learn. Have fun with it.
Like • Show 0 Likes0
Actions
- Liam Ellis @ Matt Lombard on May 30, 2011 8:50 PM
  Mark Correct
  Correct Answer
  Hey thanks Matt, another useful suggestion I'd never considered. Ive got enough information now to get a mouldable part model put together based on the expectations of the assignment. Cheers for the quick and helpful response.
  Like • Show 0 Likes0
  Actions
  - Ryan Laplante @ Liam Ellis on Mar 14, 2012 5:02 PM
    Mark Correct
    Correct Answer
    I am modifying or rebuilding the basic geometry of a countertop soda machine to be molded from plastic and this forum, the provided links and the info contined within is priceless.
    Like • Show 0 Likes0
    Actions
Josh Wood Mar 4, 2013 1:24 AM
Mark Correct
Correct Answer
Yes your model can easily be the injection molded. You can procced with it. Good luck.
_______________
micro molding
Like • Show 0 Likes0
Actions
Ant Arg Mar 5, 2013 2:01 AM
Mark Correct
Correct Answer
This part can be injection molded but it it is going to be very hard to manufacture the tooling for it. Not sure what material you are going to use but most likely polyprop. Always make a seperate configuration with your shrinkage added. That way you use the one config for you product drawings. And the other config for your mould design. NEVER forget your shrinkage. It is the dumbest mistake and you will have to tell your boss how dumb you are and everyone will laugh at you. I have created a macro that adds shrinkage and creates a seperate configuration.

Those 3mm slots will have to become 3mm cores shutting off against the cavity. That means a 3mm end mill cutter. Not gonna be easy. Unless you spark erode which is 0.2mm spark gap Which leaves you 1.1 mm and you will have to polish by hand. Not an option.

Draft analysis tool will throw you off. If you can even get it to work properly. Solidworks split line tool is also difficult to work with and its just easier to do it all by your self that way you know its correct. Last thing you want is the mould coming back full of flashing because solidworks thought everything was going to shut off niceley but it didn't.

I have used a 0.2 degree taper of injection moulded parts and its worked fine.
And you wil only need the taper on your core. Not the cavity. Remember the shrinkage makes the part stick to the core. However it is good practice to put shrinkage on your cavity.

The radii will be formed with the ball nose cutter that is used on the cnc machine. So if you want a 1mm radius then the toolmaker will use a 2 mm ball nose cutter. Bit small, rather go for a 4 or a 6. You will not notice the difference on the end product.

Those circular holes will be formed by drilling through the core and putting pins throught the holes. So getting a radius on them will be difficult. Remove the radii. It will save you a lot of trouble.

Unfortunately you learn the most form the mistakes you make. Injection moulds can be expensive. Sometimes very. And the mistakes will just add to that cost.

What i recommend... Contact a mould manufactureing plant in china. Send them the product. Get them to make you a mould for next to nothing. Let them worry about all of this. You can afford to fly there and inspect the mould for what they charge. We have had moulds delivered in 30 days for peanuts. LITERALLY.
Like • Show 0 Likes0
Actions
- Katie Maurer @ Ant Arg on Dec 2, 2015 7:59 AM
  Mark Correct
  Correct Answer
  Hey thanks Ant, your idea may be very easily to mould the tools with injection moulding..but another suggestions is with the help of art injection moulding are semi or fully automated with pick and place robots..
  Like • Show 0 Likes0
  Actions
- David Sloop @ Ant Arg on Dec 2, 2015 9:01 AM
  Mark Correct
  Correct Answer
  "Contact a mould manufactureing plant in china"
  What? Why???
  That kind of mentality is why many people (me included) had to re-invent ourselves for a career outside the plastics industry.
  I had a good ten years out of college designing plastic parts and molds, until cheap Chinese molding drew all the molding and mold building out of the US.
  Fortunately, companies found they often get what they pay for, and some of the business is coming back. Some mold shops have made a shift in service by specializing in repairing Chinese molds that wore out too quickly, or didn't produce quality parts.
  It doesn't sound like the OP is planning a career in plastics, but if he was, I'd recommend contacting a local molder, or mold builder, and picking their brain. Make a contact in the industry, and learn something.
  Like • Show 0 Likes0
  Actions
Silikon Technologies Aug 3, 2017 5:34 AM
Mark Correct
Correct Answer
Hello guys
With the years of experience in precision we manufacture silicon injection molding products that help saving our customer’s time & money. Click here to know more!
Medical Silicone Molding
Like • Show 0 Likes0
Actions

Can my model be injection molded? Take a look

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