good day (daytime greeting)Reasons and countermeasures for the large dimensional change of MC nylon due to temperature and water absorption. Here is a note about the
I will summarize what you need to understand when handling MC nylon and how to understand dimensional changes of MC nylon due to temperature and water absorption, using episodes I have actually experienced.
Dimensional change of MC Nylon
What we found out when we made a large jig for assembly with MC nylon
The other day, a relatively large piece of aluminum casting was assembledJig design We used a resin material called MC nylon at The material was specified based on the customer's past experience, but as we were assembling the finished product, we noticed something.
The mating part won't fit!
It was not that all the mating parts did not fit, but the part with the larger diameter did not fit. I did not have the equipment to measure the dimensions at that time, so I could not measure the dimensions, but it was obvious that it would not fit. I had the part corrected at the place where they machined it.
So I posed the issue to those around me via Twitter and received this response.
Quoted by v.p.
I think you mean that the amount of change is large, not disparate. There is no problem to put the dimensions within the mating intersection, but they can vary considerably depending on the room temperature and humidity at the place where the measurement is made.
Quoted by i.m.
I think I have heard that nylon has a large dimensional change with moisture and water absorption. I'm not an expert, so I'm not sure, but I'm not sure I'm going to be able to do it;
Unbalanced processing of bakes and polycarbonate boards can cause them to warp (-; -;).;
I see... I see...
The culprits of MC nylon dimensional changes are twofold.
The culprits of MC nylon dimensional changes are twofold.
- One is thermal expansion
- One is expansion due to moisture absorption
The above two points are elements of dimensional change that can occur in any material, not just MC nylon. Also, the larger the material, the greater the amount of change.
Characteristics of MC Nylon
Here, we will summarize information specific to MC nylon dimensional changes, as MC nylon is a material category and there are products that correspond to MC nylon from various material manufacturers.
coefficient of linear expansion
For reference, the coefficient of linear expansion of aluminum A5052 is "2.38 (×10^-5/°C)".You can see that the thermal expansion of MC nylon is greater than that of aluminum, which has a greater expansion.
Example of MC Nylon Thermal Expansion Calculation
Based on the above information, let us calculate the dimensional change due to thermal expansion. Let us simply find the amount of dimensional change when a 1000 mm member changes from 20°C to 40°C.
The basic formula is as follows
Dimensional change = coefficient of linear expansion x length x temperature difference
Thus, the calculation results look like this.
- Dimensional change = 0.00009 x 1000 x 20 = 1.8 mm
- Dimensional change = 9*10^-5 x 1000 x 20 = 1.8 mm
water absorption rate
The water absorption of various MC nylon grades is shown below. Only the standard grade, MC901, is listed because information on dimensional increase relative to water absorption was available. Other information could not be gathered. (We will add this information when we obtain it in the future.)
Calculation example of dimensional change of MC nylon due to water absorption
The calculation method for dimensional change due to water absorption is as follows
- Determine the amount of dimensional change relative to the water absorption before the change
- Determine the amount of dimensional change relative to water absorption after the change
- Find the difference
- The dimension multiplied by its % is the amount of dimensional change.
There is a slight problem with this: it is difficult to know what percentage of water is now absorbed.(We will add this information when we have it.)
Finally... Tips for designing jigs and other tools using resin
The above information alone may make you want to avoid using MC nylon and other resins, but resin parts are necessary when handling vulnerable workpieces. So I will leave here some tips for making jigs using MC nylon and other resins.
The first design tip
The first trick to reduce the influence of dimensional changes in resin-based designs that use fitting for centering, etc., is to make the fit as small as possible.The larger the diameter, the greater the change in dimensions, so the smaller the diameter, the less the effect.
Thus, for example, in the case of a round object jig, it is tempting to fit it with a large diameter, but instead of doing so, the method is to use positioning with a small diameter.
Second design tip.
This is a comment from someone who received this information on Twitter, but I like this idea! I thought I would share it with you.
Quoted by y@m
Our company uses a lot of processed resin products, and we use PEEK when we need to make tolerances. It depends on the equipment of the supplier, but we can get what we want.
「PEEKKah ！！！！ I see!"
PEEK properties (reference values)
Linear expansion coefficient: 4 to 4.7 (×10^-5/°C) *Up to 150°C
Water absorption (24h): 0.1-1.4 (%) *No information on leaving the product in water or at room temperature
Also,Duracon also seems to have less dimensional change relative to water absorption than MC nylon.
Properties of DURACON (reference values)
Linear expansion coefficient: 9(×10^-5/°C) *-30 to +30°C
Linear expansion coefficient: 13(×10^-5/°C) *+20 to +70°C
Water absorption (24h): 0.22 (%) *No information on leaving the product in water or at room temperature
Since there are differences in the characteristics of each product, please confirm detailed information with each material manufacturer.
Download Calculation Excel
Thank you all for the great learning experience. Thank you very much.Finally, we have also uploaded the materials we prepared for this project, so please use them in your design.
That's it.