|Milling of End Face - Course: Techniques for machining of material. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 18 p.)|
Preparations for milling end faces envisage the following:
- conceptual sequence planning for the work process for milling end faces
- selection of the commensurate milling machine (horizontal or vertical milling machine)
- selection of the milling and clamping tools, similarly also the required measuring and testing means
- positioning the necessary tools, accessories and measuring and testing means heeding the prerequisites for orderly depositing
- ensuring the functionality and safety of the tools to be used, measuring, testing equipment and accessories. Everything must be checked prior to usage. Discard worn or impaired tools must be removed.
- the milling machine envisaged for milling end faces must also be thoroughly inspected in respect of functionality and safety. Oil level control and lubrication of the milling machine shall be undertaken according to the prevailing lubrication instructions.
Clamping the tools for milling end faces
The most frequent clamping possibilities are
- clamping in the machine vice, and
- clamping directly onto the machine table (for milling end faces).
Both clamping possibilities are suited for processing the work-pieces in single or multi-piece clamping (package clamping).
Figure 10 Milling variants
(1) in the machine vice; 1 machine vice, 2 workpiece, 3
(2) directly on the milling machine table; 1 stop strip, 2 workpiece, 3 clamp
When employing the multi-piece clamping methods, ensure that the workpieces are neatly positioned alongside the stop, moreover cleanly and uniformly with the opposite side to the end face to be processed. This makes certain that all package-clamped work-pieces attain a uniform length following processing.
Figure 11 Multi-piece clamping (package clamping)
1 stop strip,
2 support surface of the milling table,
3 four workpieces superimposed,
4 clamping elements
Proper cleanliness of the workpieces is a necessary precondition for proper execution of the work process. Prior to clamping, the workpiece must be freed from chips and burrs. Metal chips inbetween the workpiece surfaces or burr on the already handled surfaces leads to surface damages (imprints) and dimensional deviations, similarly angular discrepancies in respect of the longitudinal surfaces of the workpieces.
Figure 12 Soiling when clamping the workpiece
2 soiling (i.e. metal chips),
3 stop strip
Considerable attention must be given to proper positioned determination (workpiece bearing and support surfaces) in order to attain the required angularity of the end faces to the longitudinal sides of the workpieces. The workpiece clamping means shall be aligned by means of tongues. Fine alignment of the accuracy requirements in regard to angularity with 0.02 - 0.05 mm permitted deviation over 100 mm testing length must be undertaken using a dial gauge.
Figure 13 Alignment with the dial gauge
1 dial gauge stand with dial gauge,
2 slideway to the machine stand,
3 machine vice,
4 parallel piece in the machine vice,
5 movement direction of the saddle
- When clamping the workpieces in a machine vice in order to mill end faces, it is essential to ensure that the bearing surfaces of the workpieces (parallel pieces or direct vice supports) are clean and undamaged. In this conjunction, heed the following :
. The angularity of the end faces to be milled depends on a clean workpiece support in the workpiece clamping means.
. The angularity of the end faces to be milled depends on the positional determination of the workpiece clamping means (machine vice must be angularly aligned to the slideways of the machine stand),
. The angularity of the end faces to be milled depends on the cleanliness of the workpieces to be clamped and the vice jaws. Soiling or workpiece burrs which have not been removed cause positional deviations and. thereby, lead to discrepancies in respect of the required angularity of the end faces.
- Workpiece clamping directly onto the machine table (direct clamping onto the milling machine table) ensues by means of the stop strip and chucking square.
Figure 14 Stop possibilities
(1) stop strip (flat)
(2) stop strip (angular)
Figure 15 Chucking square
The following hints must be heeded in this respect:
- The angularity of the end faces to be milled depends on the accuracy of the positional determination and stability of the stop strip.
Figure 16 Positional determination (alignment) of a stop strip using the try square
1 stop strip,
2 try square,
3 slideway to the machine stand
- The angularity of the end faces for milling depends on the cleanliness and burr-freeness of the workpieces for processing, in particular their supporting and bearing surfaces.
- The angularity of the end faces for milling depends on the positional determination of the clamped workpieces. Insufficient clamping force permits an undesired "shifting" (positional change) of the workpiece during milling. Direction of feed and of rotation of the milling tool must be so selected that the clamping pressure is directed against the stop strip. This prevents the workpiece from being shifted.
When clamping the workpieces for simultaneous milling of the end faces on a two-spindle milling machine, a portal milling device or a horizontal milling machine with a gang cutter, the following shall be heeded:
- The angularity of the end faces to be milled depends on sound positional determination and stability of the workpiece clamping means and the workpieces.
- The angularity of the end faces to be milled also depends on the cleanliness and burr-freeness of the workpiece and their clamping means.
- The workpiece clamping means (machine vice or stop strip) must be shorter (smaller) than the workpiece length required in order, thereby, to rule out damage or destruction of the clamping means and milling tools.
Figure 17 Length limitation when milling using a gang cutter
1 maximum distance between milling spindle and end support
2 milling machine arbor collar
The requirements concerning labour safety must be heeded irrespective of the workpiece clamping means used or the type of processing (single or simultaneous milling of end faces)!
In order to avoid eye injuries it is essential to employ milling protective devices or a chip catch.
When deburring the workpieces only use proper files (file handles must be undamaged and fit snugly).
Workpieces with burrs shall only be moved wearing gloves or using rags in order to avoid hand injuries.
Which workpiece clamping means can be used for milling end faces?
What must at all costs be heeded when clamping workpieces?
How can workpiece clamping means for workpieces be aligned presupposing high accuracy demands concerning angularity?
Clamping tools for milling end faces
The milling tools must be clamped securely (vibration-free). When milling using the horizontal milling machine employ short stub cutter arbors, if possible. The mill may, however, also be clamped directly to the milling spindle.
When milling on the horizontal milling machine, the milling tools should be positioned as close as possible to the milling spindle and a second end support used where long stub cutter arbors are employed.
Always wear gloves or use rags when clamping the milling tools in order to avoid hand cuts.
Which clamping possibilities are there for the milling tools for treating end faces?
What must be heeded in particular when clamping milling tools?
Selection and utilization of measuring and testing means
Use the following items in order to check the milled end faces in respect of dimensional and positional deviations:
- vernier caliper (size depends on workpiece length)
- bevelled edge square or try square
- rolled measure (for workpiece over 2000 mm long)
In order to test attained angularity of the processed end faces it is best to use the try square or bevelled edge square. Checking ensues according to the light slit method. Prior to checking clean and deburr the workpiece in order to avoid testing errors caused by soiling.
Figure 18 Test shots according to the light slit method
1 workpiece, 2 light slit (left or right), 3 workpiece is angular
Figure 19 Test errors through soiling
2 try square,
3 soiling (i.e. metal chips)
Prior to commencing work activities carefully position all measuring and testing means. Their service life depends markedly on proper handling. The measuring result shall not be mitigated by impaired measuring and testing means.