Information about automatic machines | Types and Methods
Information about automatic machines | Types and Methods
Meaning of Automatic Machines:
Automatic machines are those machines in which both the work piece handling and the metal cutting operations are performed automatically. These machines have played an important role in increasing the production rate and have been in use for long time. Initial settings have to be done very carefully, because the automatics have a fully automatic working cycle which is repeated automatically to produce duplicate parts without the participation of the operator.
In automatic machines, operations right from feeding of the stock to clamping, machining and even inspection of the work piece are carried out automatically. A particular sequence is followed depending upon the requirements of the work piece and is achieved by using cams, stops, settings, trip dogs and other mechanical movements of the machine.
All that the operator has to do during the operation is to inspect a few pieces after regular interval and plot the readings in order to study the trend of the dimensions and thereby determining the setting of the machine. He has also to renew the bar stock when it is exhausted or is to be replaced. In semi-automatic machines the movements are controlled automatically but the work has to be loaded into and removed from the chuck at the beginning and end of each cycle of operation.
Methods of Automatic Machines:
The various methods used for achieving partial or complete automatic working of the machine are described below:
(i) The suitable feeding arrangements like feed hoppers, strip feed rolls etc. could be employed on the orthodox machines to make them partially automatic in respect of material handling.
(ii) The machines used for turning operation could be made automatic in the operation of feeding and turning movement by incorporation of cams and mechanical movements, the setting of which may be made for any one of a variety of components within the capacity of the machine.
Generally one set of settings (cams etc.) is designed to suit a given set of conditions for one particular work piece only and to change from one job to other necessitates changing of all the cams, the cost of which imposes a minimum run for which the setting would be more economical than employing a more standard machine.
(iii) The third category of automatics includes machines designed specifically for operations on a particular component and generally used for drilling and profiling operations.
(iv) The fourth category includes transfer machining system in which machines are made of a collection of machining units assembled and used in conjunction with some form of conveyor or indexing work table so that the work may be automatically moved through the sequence of operations concerned.
(v) Uptil now, we have considered machines in which the actuation and control are based on mechanical movements. During recent years the concept of automatics has changed altogether due to introduction of the automatic feedback control circuits and the electronic computers.
Under the principle of feedback system the information from the element being controlled i.e. the tool or cutter is fed back electrically into the controlling system where it is compared with the set value and the tool is then accordingly moved and thus a continuous system of monitoring and corrections is used.
Classification of Automatic Machines:
Automatics may be classified according to their size, specific nature of work, type of blank machined, processing capacity, machining accuracy, design features, principle of operations, and operations performed, etc. They could be horizontal or vertical type according to the position of the main spindle. These are also classified according to the number of spindles and work positions.
The automatics are broadly classified in two main categories:
(i) Magazine Loaded Automatic Machines:
These are used to machine the work pieces in the form of blanks which have been properly machined to appropriate dimensions prior to feeding them to the automatics.
The introduction of any form of automatic feed to a machine results in economy as one operator can then attend to a number of machines instead of being confined to one.
(ii) Automatic Bar Machines:
These are used for machining work pieces from bar or pipe stock.
These are further classified as:
(a) Single Spindle Machines:
(1) Automatic cutting off machines
(2) Swiss-Type automatic screw machines
(3) Turret automatic screw machines.
(b) Multiple-Spindle Machines:
Suitable for both bar and chuck work.
Generally single spindle automates which are the logical development of the capstan and turret lathes could also be considered as below from classification point of view:
(i) Single spindle machines with movable head-stocks and fixed tools. (Also known as Swiss-type or sliding head machines).
(ii) Single spindle machines with stationary head stock and movable tools. (Also known as automatic screw machine or turret type). The Swiss-type of machine employs the ‘bush turning method’. The bar stock is fed forward by a moving head stock against a stationary tool.
During the process the bar stock is supported by a guide bush set close to the working edge of the cutting tools and thus the overhang is reduced to a minimum, and therefore, the work can be machined to very close limits.
This type of machine has the following four major parts:
(i) The sliding headstock, through which the bar stock is passed and gripped by a collet.
(ii) The tool bracket, supporting five tool slides, and guide bush for the bar stock.
(iii) The cam shaft, controlling the synchronising bar stock, and cutting tool movements.
(iv) Auxiliary attachments, for performing various operations such as drilling, tapping, screwing, screw slotting, etc.
The turret type of automatic machine has a turret with six stations. The turret is mounted on a horizontal axis at right angles to the spindle and by indexing it in clockwise direction, various tools can be presented consecutively in line with the machine spindle.
It is possible to use two or three cross-slides as well as independent swinging stops. Some special attachments are also used in order to reduce the production costs and to increase the production efficiency.
In multi-spindle automatics a number of bars of stock or components are machined simultaneously thereby increasing the production output of the machine. The number of spindles in the machine may be four, five, six or eight, but four spindle type is the one most commonly used.
In it, a separate spindle is provided for each operation and all the end tools, secured to a common horizontal turret, or end slide, work simultaneously. The spindles, carrying the stock bars, are indexed in order against each end tool station. Cross- slides, to which form tools are attached, are also fitted adjacent to each spindle.
In automatic machines, cams play the most important role and are employed to operate the various tool slides, turret and working features of automatic machines. The cams may be made from circular discs or may be of segmental form mounted on circular drums.