Fixtures-3

FIXTURES Part 3:

1 FIXTURES Part 3 Tool Design, MET3331 Dr Simin Nasseri Southern Polytechnic State University Sources: Carrlane.com Chapter 11 of SME

Modular Fixtures:

2 Modular Fixtures Modular fixtures achieve many of the advantages of a permanent tool using only a temporary setup . These workholders combine ideas and elements of permanent and general-purpose workholding.

Modular Fixturing:

3 Modular Fixturing The primary advantage of modular fixtures is that a tool can be built from a set of standard components . This has the benefits of permanent tooling ( setup reduction, durability, productivity improvements, and reduced operator decision-making ) The fixture can be disassembled when the run is complete, to allow the reuse of the components in a different fixture. At a later time the original can be readily reconstructed from drawings, instructions, and photographic records . This reuse enables the construction of a complex, high-precision tool without requiring the corresponding dedication of the fixture components.

Modular Fixturing:

4 Modular Fixturing This figure shows how modular fixturing fits into the hierarchy of workholding options, ranking below permanent fixturing yet above general-purpose workholders. 3 benefits of Modular fixturing: - Reduced lead time, - Reusability, - Versatility .

Slide 5:

5 Total quantity over tooling lifetime For applications where large numbers of parts are run on a regular basis , special purpose workholders (or dedicated workholders ) should be used. Where a moderate to small number of parts are run on a irregular basis , modular workholders may be the better choice. For small runs or one-of-a-kind simple parts, general-purpose or temporary workholders (vises, collets, chucks) may be the most economical.

Modular Fixturing- Applications:

6 Modular Fixturing- Applications One-time jobs , found especially in job shops, Jobs that do not repeat on a regular basis , For rapid setup of short-notice production runs , for prototype parts ; since prototypes are often changed or redesigned. Replacement parts are another perfect application; Trial fixturing is also an excellent application;

Tooling Plates & Blocks (subplate systems):

7 Tooling Plates & Blocks ( subplate systems ) Tooling plates and blocks are the main structural elements of any modular-fixturing system.

Tooling Plates & Blocks (subplate systems):

8 Tooling Plates & Blocks ( subplate systems ) The most elementary and basic type of modular fixturing system is the subplate system , which uses a series of flat grid plates , angle plates , multisided tooling block and similar components. Grid plate (Tooling plate) Angle plate Two-sided plate Four-sided plate Riser block

Grid Holes Vs. Earlier T-Slot Systems :

9 Grid Holes Vs. Earlier T-Slot Systems The two primary forms of modular systems available today are those with grid-pattern holes and earlier types with T slots to mount components. Grid holes offer many advantages over T slots : Modular systems with grid holes have greater positional accuracy and strength than those with T slots. T-slot systems permit movement along the slot , so nothing but friction holds components in place. Wherever T slots cross each other , a weak point exists . T-slot modular fixture Grid holes

Multipurpose Grid Holes Offer Maximum Flexibility :

10 Multipurpose Grid Holes Offer Maximum Flexibility Grid-pattern modular-fixturing systems come in two styles: those with alternating dowel holes and tapped holes (dowel pin bushing next to threaded insert) and those with multipurpose holes ( click here ) . The alternating-hole style does not offer as many advantages as the multipurpose-hole style. Multipurpose holes have both an alignment bushing and threaded insert in the same hole. This arrangement permits each hole to serve as an alignment hole, mounting hole , or both .

Multipurpose Holes:

11 Multipurpose Holes Locating screws are used to locate and fasten at the same time. Multipurpose holes will accept socket-head cap screws, studs and locating screws and many other threaded components. Stud Socket-head cap screws

Choice of Three System Sizes:

12 Choice of Three System Sizes A good modular fixturing system needs to accommodate a wide range of workpiece sizes. Carr Lane offers a full line of modular components in three system sizes . As a comparison to choose the proper system size, the table below shows typical clamping force exerted by clamp straps in each size (2-to-1 lever ratio).

Grid Address System:

13 Grid Address System Standard & heavy The grid pattern of multipurpose holes on every tooling plate and tooling block face is labeled with letters in one direction and numbers in the perpendicular direction . Tooling-block faces are numbered (counterclockwise) with Roman numerals. This allows recording the mounting-hole location of each component (e.g., A2, B3, D7, etc.) as part of permanent documentation. Multipurpose holes are spaced within ±.0008 inches of true position on all tooling plates and blocks . The mini system is even more accurate, with all holes spaced within ±.0004 inches . Mini

Mounting Tooling Plates on T-slotted tables:

14 Mounting Tooling Plates on T-slotted tables Standard and heavy rectangular tooling plates are accurately located on T-slotted tables using two Locating Keys ( click here ) in the center table slot. These plates are fastened to the machine table using four or six socket-head cap screws and T Nuts . How do we locate the tooling plates on the machine table?

Slide 15:

15 Mounting Tooling Plates on T-slotted tables Mini-size rectangular tooling plates are accurately located on T-slotted tables using two Sure-Lock Fixture Keys in the center table slot. These plates are normally fastened to the machine table using two or three socket-head cap screws and T Nuts . Alternatively, four Forged Adjustable Clamps can be used for greater holding force. Click on the lock

Mounting Tooling Plates on Subplates:

16 Mounting Tooling Plates on Subplates In this case, Subplate Locating Keys are used for location. A round key and a diamond (relieved) key are used together for precise location without binding. The subplate hole pattern shown here allows mounting any size and combination of standard or heavy rectangular tooling plates, either lengthwise or widthwise.

Mounting Tooling Plates & Blocks on Pallets:

17 Mounting Tooling Plates & Blocks on Pallets JIS-type mounting is the most-common way to mount tooling plates and blocks on a machining-center pallet. Here the plate or block is located from two precisely ground reference edges at 90° to each other. The plate or block is pulled against the pallet's edge locators using three socket-head cap screws and also fastened down with four to eight socket-head cap screws, depending on the size. Swivel Hoist Rings are recommended for lifting tooling blocks and large tooling plates. Just for your information

Slide 18:

18 Mounting Tooling Plates & Blocks on Pallets Most of Carrlane’s modular tooling plates and blocks also incorporate DIN-mounting capability . Here the plate or block is located using a center hole, and oriented using a radial hole. Two Pallet Fixture Keys, a center pin and a radial pin, are required. The plate or block is fastened down with four to eight socket-head cap screws, depending on the size. Just for your information

Modular Fixturing Bill of Material:

19 Modular Fixturing Bill of Material

Test yourself!:

20 Test yourself! What are the differences between a permanent fixture and a modular fixture? In many ways modular fixturing is just like permanent fixturing, except for a few key differences. First, modular fixtures can be assembled entirely from reusable off-the-shelf components , without machining. Next, many modular components are adjustable and universal . Finally, specially designed tooling plates and blocks, with a standard grid pattern , are the foundation of a good modular system.

Cool Design!:

21 Cool Design! Vs bad design

Problem:

22 Problem A tool designer is requested to design a fixture to locate a workpiece (shown below) for milling the top surface. When the clamps were tightened, the clamping action actually deformed the basic shape of the part ! After machining, when the part was released, it returned to its unclamped shape, resulting in a machined surface that is concave rather than flat! What could be the solution for this problem? He decided to choose two strap clamps to hold the two edges of the workpiece. ?!

How to avoid the distortion in the part:

23 How to avoid the distortion in the part Modular workholding components are designed for optimal clamping of parts with the least possible distortion using ball pads to support the workpiece . These ball pads are flexible and align themselves to the contour of the workpiece . The clamping bars also have ball pads; therefore, distortion of the part is practically eliminated. www.ame.com