OMNIAPLASTICA
Machining and Tolerances
The fact that plastic materials are softer than steel does not mean
that they are easier to cut, drill or machine.
The most important problem is the loss of heat accumulated because of
the tool friction. The plastic materials are bad heat conductors, so
the heat accumulated during machining, causes internal stresses into
the semifinished products and they may break or lose part of their mechanical
features.
Furthermore the presence of overheated areas caused by machining, prevents
to obtain the requested tolerances
TOOLS : you can use the same tools as for steel but they must be sharp and clean. For glass-filled materials it is advisable to use carbide tips.
COOLING: abundant use of a coolant during all stages of machining is most important. An increase in temperature through friction causes either breakage of the plastic item or a build - up of hidden internal stresses which are dangerous for the application.
TEMPERATURES: the plastic piece must not be cold when you machine it. You are advised to pre-heat the piece to about 50°C prior to machining, in order to reduce the operating times.
SPEED: a low speed of travel together with sharp tools will result in a machined part free of stress. Too high a speed will cause overheating with either visible or hidden stresses.
TURNING: use the same type of tools as you would for metals, the only exception being that for glass-filled plastics: you must use carbide tips.
DRILLING: this is the most critical operation as it causes excessive heat build-up and stresses. Use sharp drills and abundant cooling. Remove swarf frequently. Start by drilling a small hole ( max diam. 15 - 20 mm ) and then gradually step-up to the diameter you require.
MILLING: use the same type of tools as you would for metals. They must be sharp. Use abundant cooling liquid.
CUTTING: bans saw can be used but circular saws with tipped blades are more suitable (teeth having a pitch of 20 - 25 mm).
 |
TURNING | PA | PA GF | PET POM |
PE | PTFE |
|---|---|---|---|---|---|---|
| Speed m / min | 200 ÷ 400 | 300 ÷ 500 | 300 ÷ 500 | 250 ÷ 400 | 150 ÷ 250 | |
| mm / U | 0,1 ÷ 0,3 | 0,1 ÷ 0,2 | 0,1 ÷ 0,5 | 0,2 ÷ 0,5 | 0,1 ÷ 0,3 | |
| a | 0 ÷ 5° | 0 ÷ 5° | 0 ÷ 5° | 0 ÷ 5° | 0 ÷ 5° | |
| b | 5 ÷ 15° | 5 ÷ 10° | 5 ÷ 10° | 5 ÷ 10° | 5 ÷ 12° | |
 |
DRILLING | PA | PA GF | PET POM |
PE | PTFE |
| Speed m / min |
50 ÷ 100 | 50 ÷ 100 | 50 ÷ 100 | 100 ÷ 200 | 150 ÷ 250 | |
| mm / U | 0,1 ÷ 0,4 | 0,01 ÷ 0,1 | 0,01 ÷ 0,2 | 0,1 ÷ 0,3 | 0,2 ÷ 0,6 | |
| a | 10 ÷ 20° | 15 ÷ 30° | 15 ÷ 30° | 10 ÷ 30° | 5 ÷ 20° | |
| b | 60 ÷ 100° | 60 ÷ 90° | 60 ÷ 90° | 60 ÷ 90° | 110 ÷ 130° | |
| g | 5 ÷ 12° | 5 ÷ 10° | 5 ÷ 10° | 10 ÷ 15° | 10 ÷ 15° | |
 |
MILLING | PA | PA GF | PETPOM | PE | PTFE |
| Speed m / min |
< 1000 | < 1000 | < 1000 | < 1000 | < 800 | |
| mm / s. tooth |
< 0,4 | < 0,4 | < 0,4 | < 0, 6 | < 0,5 | |
| a | 5 ÷ 15° | 5 ÷ 10° | 5 ÷ 10° | 10 ÷ 20° | 10 ÷ 20° | |
| b | 5 ÷ 15° | 5 ÷ 15° | 5 ÷ 15° | 5 ÷ 15° | 5 ÷ 15° | |
|
CUTTING | PA | PA GF | PET POM |
PE | PTFE |
| Speed m / min |
~ 3000 | ~ 3000 | ~ 3000 | ~ 3000 | ~ 2000 | |
| D mm |
15 ÷ 40 | 15 ÷ 40 | 15 ÷ 40 | 15 ÷ 40 | 15 ÷ 40 | |
| a | 0 ÷ 5° | 0 ÷ 5° | 0 ÷ 5° | 0 ÷ 5° | 0 ÷ 10° | |
|
CUTTING | PA | PA GF | PET POM |
PE | PTFE |
| Speed m / min |
400 ÷ 800 | 400 ÷ 800 | 500 ÷ 900 | 500 ÷ 900 | 300 ÷ 600 | |
| K mm |
5 ÷ 10 | 5 ÷ 10 | 5 ÷ 10 | 5 ÷ 10 | 2 ÷ 5 | |
| b | 0 ÷ 5° | 0 ÷ 5° | 0 ÷ 5° | 0 ÷ 10° | 0 ÷ 10° |
OBTAINABLE MACHINING TOLERANCES
Because of the elasticity of plastics and their reaction to temperature
and humidity it is impossible to obtain tight tolerances with all materials.
It is useless to machine high precision pieces when their tolerances
are deleted because of the normal temperature variations and air moisture
content.
Contrary to metals, it is often too expensive and useless to obtain tight
tolerances from a plastic part due to the physical properties of plastics.
The schedule gives only indicative values on the stable tolerances obtained
by different materials for some dimensions.
Calculations are based on temperature variations of 30°C. (from 20
to 50 °C) and humidity variations from 0 to 50%. The transverse lines
show the stable tolerance limit considering the scheduled variations
of temperature and humidity for the different materials.
The tolerance values shown in the left are difficult to be kept.
Obtainable tolerances referred to ISO R286. The data and the informations
are supplied without engagement from our part.
Omnia Plastica technical office is at your disposal for further explanations.
Please don't hesitate to contact us four your needs