Vacuum Workholding Expertise
Thame Workholding has built up a wealth of experience providing standard and special workholding solutions to all sectors of industrial manufacturing using vacuum.
In particular the aerospace, medical, motorsport, electronics and precision sub-contracting industries have many successful working vacuum applications supplied by us.
Vacuum workholding is a highly effective technique for holding thin, irregular shaped or non magnetic parts. Although parts with a large surface area are ideal, as the holding force is also large, there are also techniques for holding small parts. Vacuum workholding can be applied in milling, turning, grinding and drilling applications.
Vac-Mat fixtures transfer the vacuum to many suckers on a replaceable synthetic mat. Each sucker helps to hold the part flat against the fixture. The mat can be cut into by the milling tool to finish machine the edges or produce a window or pocket on the part. The entire mat does not need to be covered as it still maintains the holding power when up to 50% is exposed.
Informational Video: click here
Grid plates are suitable for batches of rectangular or square parts which have no through holes, especially where a high degree of parallelism is required. The work piece is clamped to the fixture by the vacuum created within the sealed grid pattern area; this fixture will accept heavier machining then most other types of vacuum fixtures. Standard and special size grids are available.
Sintered Metal and Metapor© Fixtures
Sintered metal and Metapor fixtures have a porous surface area made out of sintered bronze, ceramic or porous aluminium depending on the work piece type and application. Metapor© opens up a new perspective for different vacuum clamping solutions.
Rotary Vacuum Chucks
Rotary vacuum chucks offer a wide scope of application for thin-walled parts as well as aluminium and plastic parts, etc. without causing distortion or clamping marks. Systems can be designed for CNC turning machines, grinding machines and lathes with through spindles. Rotary chucks can, if required, go up to 6000rpm.
Flip-Pod Vacuum Fixtures
The flip-pod vacuum fixture is a modular vacuum clamping system that is especially good for machining plastic, wood, glass and non-ferrous metals. Used in CNC milling, routing, de-burring and drilling operations. The pods activate on being ‘flipped’ and self store or nest when not in use. When in the raised position the work piece can be accessed around it edges and drilled through if required. The system reduces set-up times between work piece changeovers and thereby increases productivity. Systems are designed to suit work piece requirements.
Slot Vacuum Fixtures
Slot vacuum fixtures are extremely light and thin fixture plates that are made from anodised high tensile aluminium and are especially suited for small parts during light milling and drilling and all kinds of engraving. Rubber adaptor mats are used to permit fast changeovers and offer high slip resistance to the work piece. Plate sizes range from 150 x 100 x 28 up to 600 x 400 x 28mm.
Vacuum Operating Systems and Accessories
We offer a very wide range of vacuum operating equipment including a vacuum pumps to operate different types of vacuum fixtures. Other accessories including gauges, vacuum seals, hoses, filters, rotation joints, distributors, vacuum grease, etc are available.
Special Vacuum Packages
From large fixtures for gantry milling machines to CNC high precision turning machines and 3D shape fixtures, we use our wealth of experience to design and manufacture vacuum workholding solutions to suit all types of applications. Working with our partners Horst Witte, we are at the forefront of vacuum workholding technology.
Vacuum Workholding – How Does It Work?
On all surfaces of an object there is an even pressure due to the surrounding atmosphere of approximately 1 bar (10.9kg per square metre or 14.5 pounds per square inch). Using a vacuum pump, the air beneath the component is sucked away, so the pressure load on these lower surfaces is partly removed; the clamping or holding force results from the difference in pressure between the upper and lower component surfaces.
The amount of one-sided pressure is dependent on the amount of under pressure or vacuum generated. Modern vacuum pumps reach a vacuum of approximately 990mbar (20mbar absolute or 98% of the atmospheric air pressure of about 1 bar.)
Using this theoretical example the pressure remaining on the lower surface is approximately 20mbar, the material is held down by the difference between the upper and lower pressure.
The weather and position above sea level of the vacuum application will have an effect on the actual clamping force obtained for a specific application.
Vacumm Workholding – What Hold Down Force Can I Achieve?
The clamping force on a component is proportional to the surface area, therefore for a component size of 20cm x 40cm and vacuum of 0.8 bar, the clamping force can be calculated: (1 Bar = 100kN/m² or 14.5lbs/in²)
Clamping force in kN/m² is 0.20m x 0.40m x 0.8bar x 100kN/m² = 6.4kN
Clamping force in lbs/in2 is 7.87” x 15.75” x 0.8bar x 14.5lbs/in² = 1437.8lbs
Machining Guide Lines
When using vacuum to hold parts it may be necessary to review the machining process to suit this style of workholding. Vacuum workholding is less effective on small size components therefore rather than machining individual work pieces, plan to machine several parts from a larger size of raw material.
Cutting tool technique when using vacuum fixtures tends to mean using smaller diameter cutters, increasing spindle speeds, feed rates and ramping rather than plunging. Cutting forces need to be considered and on thicker material it may be necessary to employ the use of stops directing the cutting tool pressure toward the stop. Unsuitable or blunt tools increase cutting force pressure and should be avoided.
Applications and Advantages
We offer Vacuum Workholding for the following:-
- Horizontal and vertical milling machines
- Machining centres with or without pallets
- Turning machines, manual or CNC
- Grinding machines, surface and cylindrical
- Engraving machines
- Measuring machines
- Special purpose machines and applications
Vacuum workholding offers the following benefits:-
- Clamping with no distortion or clamping marks
- Very fast clamp and un-clamp cycle time
- Machining without vibration, thus preventing chatter marks
- Machining area free of clamps for possible multi-surface working
- Suitable for many materials
- Adaptable to many different processes
Downloadable PDF: Vacuum Workholding