Broaching Machine.pptx

broaching

1. Broaching Machine

2. BASIC PRINCIPLES OF BROACHINING Broaching is a machining process for removal of a layer of material of desired width and depth usually in one stroke by a slender rod or bar type cutter having a series of cutting edges with gradually increased protrusion as indicated in Fig .

3. BROACHING Broach is bar type cutter with series of cutting edges gradually increasing in size to remove all materials in one stroke. In broaching there is only one motion, i.e. the primary cutting motion is provided by the machine, where as the feed is obtained by placing the teeth progressively deeper. Since there is no feed motion, the shape of the broach determines the shape of the machined part . Broach is used to produce internal forms like spline holes, non-circular holes, slots, grooves, gears etc. Internal broaching is done by either pulling (or) pushing the broach through a hole drilled in the work piece. Pulling is highly preferred to facilitate alignment and avoid buckling.

4. External forms can also be produced by using pot broach . Here the broach is made in segments and fixed inside a fixture called pot fixture. The broach is stationary but the W.P. is pulled / pushed through it.

5. Advantages Both roughening and finishing operations are completed in one pass of the tool. Any form that can be reproduced on a broaching tool can be machined by broaching process. Rate of production is high, because the actual cutting time is a matter of few seconds only. Rapid loading and unloading of fixtures keeps the total production time to minimum. Internal and external surfaces can be machined within close tolerances. Accuracy of surface finish is of the order of 0.1 micron. The operation of broaching is simple and there exists a possibility of automating the process. Broaches have exceptionally long life since each tooth of a broach passes through or over the work only once per pass. A broad range of materials are successfully broached with proper broach design and setup conditions.

6. Disadvantages The tooling cost is very high and hence broaching process is adopted only in those places where mass production is required. The broaching tool is made for a particular job only and cannot be easily adopted to a range of applications. Surfaces to be broached should not have any obstruction. Work-piece to be broached should be rigid and strong to withstand heavy tool forces encountered during cutting operation. The process of broaching is not recommended for the removal of large amount of stock and short run jobs. All the elements of the broached surfaces must be parallel to the axis of the travel. Obviously it is not possible to broach the entire surface of a tapered hole.

7. ADVANTAGES AND LIMITATIONS OF BROACHING Major advantages • Very high production rate (much higher than milling, planing , boring etc.) • High dimensional and form accuracy and surface finish of the product • Roughing and finishing in single stroke of the same cutter • Needs only one motion (cutting), so design, construction, operation and control are simpler • Extremely suitable and economic for mass production Limitations • Only through holes and surfaces can be machined • Usable only for light cuts, i.e. low chip load and unhard materials • Cutting speed cannot be high • Defects or damages in the broach (cutting edges) severely affect product quality • Design, manufacture and restoration of the broaches are difficult and expensive • Separate broach has to be procured and used whenever size, shape and geometry of the job changes • Economic only when the production volume is large.

8. Classification There are different types of broaching machines which are broadly classified • According to purpose of use Δ general purpose Δ single purpose Δ special purpose • According to nature of work Δ internal broaching Δ external (surface) broaching • According to configuration Δ horizontal Δ vertical • According to number of slides or stations Δ single station type Δ multiple station type Δ indexing type • According to tool / work motion Δ intermittent (one job at a time) type Δ continuous type

9. Horizontal broaching machine Horizontal broaching machines, typically shown in Fig ., are the most versatile in application and performance and hence are most widely employed for various types of production. These are used for internal broaching but external broaching work are also possible. The horizontal broaching machines are usually hydraulically driven and occupies large floor space .

10. Vertical broaching machine Vertical broaching machines, typically shown in Fig ., occupies less floor space are more rigid as the ram is supported by base Δ mostly used for external or surface broaching though internal broaching is also possible and occasionally done .

11. High production broaching machines (continuous broaching machine) Broaching operation and broaching machines are as such high productive but its speed of production is further enhanced by; Δ incorporating automation in tool – job mounting and releasing Δ increasing number of workstations or slides for simultaneous multiple production Δ quick changing the broach by turret indexing Δ continuity of working methods of continuous broaching is used for fast production of large number of pieces by surface broaching .

12. SAWING MACHINE Before metal is presented to a machine tool it is usually cut to some specified length and operation of cutting is generally performed by sawing . Metal sawing is chiefly concerned with cutting bar stock to convenient length or size for machining. In sawing, the individual tooth of the saw tracks through the work, in each tooth deepening the cut made by the proceeding teeth in the direction of feed. Either the saw or work may be fed and, by controlling the direction of feed, either straight or curved cut can be produced. The width of cut is approximately equal to the width of the saw itself.

13. Classification of sawing machines The sawing machines are broadly classified as: (i) Band saw, (ii) Circular saw (iii) Reciprocating saw

14. Band Saw Originally band saw was used for serving work-pieces and doing rough contour sawing. But modern band saw of today is a precision machine capable of performing a variety of operations quite accurately. These machines are more expensive that hack-saw but are capable of faster cutting because of continuous action. Larger number of teeth, only a few in contact with the work at a given time, allow high surface speeds since the teeth cool off during their travel. A big advantages of band sawing machines is contouring ability and thus intricate curved shapes can be cut by a combination of hand and power feeds.

15. Circular saw It is called Circular saw as it has a circular blade with inserted teeth for cutting small or large bars to desired length. It has many of the characteristics of an inserted tooth milling cutter, although it is of much larger diameter. It runs at relative slow speed and is very powerful. Coolants may or may not be used with this type of saw.

16. Reciprocating Saw Several bars may be cut at the same time and continuous attention is not needed since the saw will shut off automatically when the cut is finished. A lubricant is often used for easier cutting action and longer blade life. A crank mechanism is provided to raise the blade on each return stroke so that teeth are not damaged by being dragged backward over the work. It is important to note the provision of dash pot mechanism by a cylinder and piston filled with viscous oil and connected between the base and reciprocating arm carrying the blade. It avoids the rapid wear of blade teeth, thereby increasing the blade life. It provides a relatively slow and expensive method of cutting.