Kicking Tee - Predicting Injection Moulding with SOLIDWORKS Plastics

Friday July 30, 2021 at 3:45pm
For our second challenge in our Rugby Lions themed competition with South African reseller MECAD we modelled an adjustable kicking tee, now we want to take things a step further and make sure our design is prepared for manufacture.

The kicking tee consists of two parts that are going to be injection moulded using a low-density plastic, in this blog we will use SOLIDWORKS Plastics to analyze the parts to ensure that they can be manufactured without defects and can fit together correctly after accounting for shrinkage.

First take a quick look at the design of the two parts.
Kicking Tee - Predicting Injection Moulding with S


MOULD SUITABILITY ANALYSIS


Before we begin the plastic analysis we will check that these parts are viable for injection moulding by using the built-in tools inside SOLIDWORKS to check draft angle and thickness.

Below we can see positive and negative draft in red and green however we can also see on this model the ribs currently have no draft. So, depending on the location of the parting line this maybe something we need to address to ensure we can get the product out of the mould.

We can also check for undercuts and run a thickness analysis to check for regions which maybe too thin or too thick. Thin wall sections will cool much faster and will generally harden first. Whereas sections that are too thick can take a lot longer to cool and cause sink marks or warp. Ideally the wall thickness will be as uniform as possible.

So, from these quick checks we can see that we could make some improvements to this part for injection moulding. We could add more draft in certain areas and look to reduce some of the thick regions for a more uniform wall thickness. But let’s put it into SOLIDWORKS Plastics to see if we could mould this design.

In this case we will start by moulding each part separately but later in the design we could look to create the runner system and the full moud layout. Or even look at over moulding on this model.

PLASTIC ANALYSIS - TOP PART


The set up in SOLIDWORKS plastics is quick and easy we just need to select our material from the HUGE plastics database. This contains a lot of the information we need such as viscosity, melt temperatures, suggested mould temperatures, Young's modulus, thermal expansion coefficient, density, fiber percentage and much more. Once we have done that, we just set the basic parameters for our machine and then pick our desired injection location.

On the top part of the tee we will pick underneath the model. This region is out of sight when the rugby tee is assembled. We can even quickly view the predicted flow pattern at this point to help us decide on the best location or multiple locations if required.

Next all we have to do is run the study, this study took minutes to run and from this we can see straight away from the ease of fill plot if this will fill on our machine using our selected material. In this case we can easily fill this geometry.

We can plot pressure in more detail as well if required. Either at the end of the fill stage or the end of the packing stage:

We can also gain an understanding how the plastic will behave as it fills the cavity by reviewing the fill plot animation. This gives great insight even more so than watching the actual moulding process - unless you had a transparent mould!

However now we know the model will fill at this point we are interested to see how the geometry will look after the moulding process to see if it will fit the lower part of this model. To do this we can first review the total stress displacement plot:

Here we can see the model is going to shrink inwards. This could cause issues with the thread fit on the other model, to check this we will export the deformed shapes and run an interference detection.

PLASTIC ANALYSIS - BASE PART



Before we can export the deformed shapes, we need to repeat the above process for the bottom part of the Tee. Lets skip forward to reviewing the results of the study.

Here we can see this part will fill in around 3.2 seconds.


And it will fill within our machine pressure tolerance of 100Mpa:

But again we can see on this part there is considerable shrinkage:

Looking more closely, this model isn’t perfect as there are some sink marks, air traps and weld-lines. We won't touch on them now but normally we would might consider them in further studies.

The final step now is to export the deformed shape of both studies and see if they now fit together without any significant interferences. In the short video below you can see us switch from the designed part to the deformed shape, which is the shrunken version, after switching we check for interferences.

Here we can see there are no interferences present with our current tolerances. This is largely because both parts are made of the same material. So the final step is to see if the ball will balance on our final tee using SOLIDWORKS motion analysis!

MORE RUGBY LIONS


Check out how MECAD designed their kicking tee using XDESIGN a cloud based Sub-Division modeller that links directly with SOLIDWORKS and is perfect for creating organic shapes quickly.

We'll be posting again soon about how we used SOLIDWORKS Plastics to optimize the manufacturing parameters for our kicking tee so check back shortly! Next week we will move onto our third and final challenge, creating the Rugby Lions Trophy!

Finally we will be hosting a joint tips and tricks webcast with MECAD using all the models we've created for these challenges on August 6th, we will share more modelling advice as well as showing how we created the renders and animations using SOLIDWORKS Visualize and more. We hope this will be useful to any SOLIDWORKS user so if you're interested please sign up here!

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