Common problems with 5-Axis Machining Centre and how to avoid them
5-Axis Machining Centre is a machining centre that can orient the cutter or the workpiece on two additional rotary axes. It is used for parts with compound angles, deep cavities and features that would otherwise need several setups. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.
It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, oil and gas is used as the example: materials that work harden and still have to be certified.
The problems that actually occur
These are the failures that show up on a real job, listed in the order in which they are usually discovered.
- The tool centre point not compensated, so the length is wrong as soon as the head tilts. The cause is usually upstream: a datum that is not the functional one, a fixture that does not repeat, or a specification that cannot be measured the way it is written.
- Collision between the holder and the part, which only shows up in a simulation. The cause is usually upstream: a datum that is not the functional one, a fixture that does not repeat, or a specification that cannot be measured the way it is written.
What causes them
In most cases the cause is upstream of the operation, not in it. The tool centre point not compensated, so the length is wrong as soon as the head tilts is usually a symptom of one of the three causes above rather than a problem in its own right.
How they are prevented
Prevention is duller than diagnosis. Avoid deep narrow cavities that force a long thin holder, and the result is confirmed by CMM with a five axis probe head, or structured light scanning for free form faces before the batch is released.
| Item | Note |
|---|---|
| Failure | the tool centre point not compensated, so the length is wrong as soon as the head tilts |
| Prevention | avoid deep narrow cavities that force a long thin holder |
| Tolerance to hold | ±0.01 mm |
| Finish to check | Ra 0.8 µm achievable with a finishing pass |
Applications
5-Axis Machining Centre is used for parts with compound angles, deep cavities and features that would otherwise need several setups, and in practice it appears most often in impellers and blisks, aerospace structural parts, medical implant trials, mould cores.
How it fits into a machining route
5-Axis Machining Centre is one station in a route rather than the whole of it. The part arrives with the previous operation finished and leaves with the features it is responsible for completed, so the datum and the clamping method are agreed before the first part rather than discovered on it.The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: programming time and simulation, not machine hourly rate. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.
Standards, documentation and what is issued
The documentation requirement is AS9100 with material traceability. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.
CMM with a five axis probe head, or structured light scanning for free form faces is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.
Frequently asked questions
What tolerance should be specified for 5-Axis Machining Centre?
±0.01 mm is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.
Which material is usually used?
Ti-6Al-4V titanium is the usual choice, supplied against AS9100 with material traceability.
How is the result verified?
CMM with a five axis probe head, or structured light scanning for free form faces, with the results recorded so a repeat order can be compared with the first.
What is the most common mistake?
Collision between the holder and the part, which only shows up in a simulation.
How long does it take and what does it cost?
A realistic cycle is 40 to 120 minutes for a complex part, and the cost driver is programming time and simulation, not machine hourly rate.
Related capability
If you are specifying 5-Axis Machining Centre on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.
Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.
Related entries
These entries sit next to 5-Axis Machining Centre in the encyclopedia: Swiss-Type Lathe, Turn-Mill Centre, Lapping. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
