We will now study the various components, mechanisms and accessories employed in the plastic bucket heat transfer machine.
- Machine Design:
It is very difficult to lay down any hard and fast rules regarding the design and layout of transfer machining lines because these will differ according to the component involved and the nature of operations to be carried out.
In general, the machines consist of simple heads incorporating minimum mechanism. These may also incorporate provision for multi-spindle attachments, may be provided with hand feed for setting purposes, automatic feed and withdrawal mechanism. They may also incorporate a lead screw for thread tapping purposes. The feed cycle often provides for fast approach and quick withdrawal.
Each head is generally a self-contained unit and can be operated as such when setting up, but is connected either electrically, mechanically etc., with other machines so that it operates in unison with them, i.e. the cycle of each machine commences simultaneously with those of others.
The machine is required to perform following functions:
(i) Transfer the work from station to station.
(ii) Locate the fixture at each station and clamp it in position.
(iii) Move the tools rapidly to the work for the approach portion of the machine time.
(iv) Move the tools slowly into the work for the cutting portion of the cycle.
(v) Return the tools rapidly to clear the work.
(vi) Unclamp the work from the fixture and indicate that the station is clear for operating on the next work piece.
The operations which it is usually required to perform are:
(h) Face milling,
(j) Hollow milling,
(m) Air pressure testing,
(n) Blowing out or dumping chips,
(o) Rolling over or revolving work.
The heads are mounted on one or more sides of a long table on which the work is carried. The table usually consists of rails, a static roller conveyor track, or a combination of both and its frame carries the mechanism for transferring the work from one station to other. The table is generally straight, although in some cases it may be circular, U-shape, curve forward and backwards or of any other shape to suit local conditions.
Generally roll-overs are also provided in the table line so that components could be rotated through 90 to 180° during its progress from station to station, if need be. Arrangements may also be provided for transferring the components to an auxiliary line or to a machine not built into the table. For fully automatic installations use of shuttle operated either pneumatically or hydraulically could be made for moving the work from one position to another.
III. Work Holding:
Although large and flat components can often rest directly on the surface of the table, but it is generally more convenient to mount the work on platen, pallet or jig plate etc. which are specially designed to suit the components they carry.
These are provided with some form of clamping device for securing the work to be carried and also incorporate means for locating the components on its carrier and often for locating the carrier under the various machines. The underside is designed to suit the type of table and may be flat for riding on rollers or recessed to suit vee or flat rails.
- Transfer Mechanism:
A wide variety of transfer mechanisms are available for moving the platen from station to station. It is to be noted that the distance between the centres of all the machine heads must be identical, and that the stroke and position of the transfer pawls must be arranged to deliver every platen to a precise position under each machine.
The system should also be inter-connected with the time cycle of the machines and interlocks or other means provided to ensure that the platens are not moved until the last tool is clear of the work, or that the spindles cannot descend until the transfer movement is completed.
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