|Cutting by Milling - Course: Techniques for machining of material. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 17 p.)|
Before cutting the workpieces delivered as bar stock material, one side of the bar should be processed by end milling. Thereat the cutting depth should be chosen so that with a least chip removal the end face will be clean milled. By means of the end milling, a workpiece cut-off (loss of material) is not necessary. The end milling should be carried out on all delivered bars by means of multi-piece clamping on a horizontal milling machine. With the cutting by milling of rotationally symmetrical (cylinder-shaped) workpieces prism slide jaws (prism slide lengthwise) for the clamping in a machine vice are applied.
In some cases the cutting by milling is also carried out after marking. This is done mainly at workpieces where, after cutting by milling, surfaces are resulting being not in an angle of 90° to the reference face. So they have no parallel faces to the opposite face either. These workpiece shapes do often result from cutting by milling of collars in the form of different segments.
Figure 11 - Cutting after marking
1 - workpiece with marking
2 - segments
The fixing (localization) of workpieces after marking is done by means of a marking gauge where the working face is slid along the face of the machine table or e.g. also along the glide path of the machine stand by hand.
Because of their small cross section metal slitting saw blades are tender milling tools:
- A too high speed of rotation leads to a premature dulling (wear) and so to a degeneration of the surface quality of the workpieces.
- A further application of dull metal slitting saw blades can lead to a "standstill" during the cutting process and so to a breakage of the metal slitting saw blade. By a "standstill" of the metal slitting saw blade we do understand the situation when at a working table feed in the working direction and the cutter arbor rotating, the metal slitting saw blade is not moving any longer. This situation can be explained by a non-positive connection, not a positive one as usual with other milling tools.
- The application of metal slitting saw blades of a larger diameter (250 to 300 mm) can lead to the untrue running of the metal slitting saw blade. This means that the metal slitting saw blade is pushed away during the cutting process sidewards because of its' small cross section.
This results in uneven and non-angular or non-parallel surfaces on the workplace. Moreover, the risk of breaking (breakage) of the metal slitting saw blade is increased. In order to counteract this with the application of metal slitting saw blades of larger diameter and smaller width chuck flanges are fastened on both sides of the metal slitting saw blade (see figure 8).
The setting-up of the milling machine to carry out the technique cutting by milling is done according to the following sequence of operations:
- Checking the completeness and functioning of the milling machine, of the clamping means and auxiliaries to be applied, oil-level check and lubrication of the milling machine to be carried out according to the lubrication schedule's cycle.
- Arrangement of the necessary measuring and testing means at the workplace on a suitable soft base.
- Chucking and fixing of the clamping means.
- Setting-up and clamping in or on the workpiece (workpiece support, length feed stop).
- Fixing the coolant system when processing workpieces made of steel.
- Installing of the milling protective system.
- Clamping in the cutter arbor and clamping on the metal slitting saw blade. Do not forget the feather key in one of the arbor rings!
- Positioning of the milling machine table into the appropriate processing position to the milling tool (X-Y-Z-direction).
- Fixing the cutting values (speed of rotation, feeding speed) according to the indications given on the nomogram or in a table for the appropriate milling machine. The cutting depth at cutting by milling corresponds to the width or height or the workpiece.
- Cutting by milling is carried out as conventional milling. The plunge milling is applied only in exceptional cases. Cutting by milling of non-metallic raw materials (e.g. plastics) as down-cut milling is applied very seldom, too.
- Cutting in (a small groove in the workpiece) at the rotating metal slitting saw blade. Table feed back and make a dimensional inspection of the workpiece in the fastened condition. If necessary, correct with manual adjustment of the head.
- Continuation of cutting by milling using a strong jet of cooling water directed on the place of the cutting by milling.
- Clamping out, deburring and cleaning of the workpiece, linear measure control and control of the angularity and surface finish.
- If necessary, make corrections on the localization of the workpiece or the clamping means, and on the linear or space measures to the reference face.
- With the change of the workpieces you should meet the requirements of a proper clamping of the workpieces (burr-freeness, cleanliness of the workpiece supporting and bearing surfaces).
Permanent control of the workpiece on adherence to the quality requirements secures a continuous production process and helps to avoid rejects (uselessness of the workpieces).
- Ending up with the technique of cutting by milling you should clean the milling machine, all tools used, auxiliaries and the whole workplace. The used metal slitting saw blades are sent on to be resharpened (sharpen).
What is the task of the feather key in one of the arbor rings
between the metal slitting saw blade and the arbor
What are workpieces with a marking fixed with for cutting by
Which milling process is usually applied on cutting by
What is the purpose of "clean milling" of bar stock material at
one end face before cutting by
What is always necessary at the end of cutting by