Design and application of universal adjustable fix

2022-08-22
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Design and application of universal adjustable fixture for drilling shift shaft of transmission

there are many kinds of shift shaft products in automobile transmission with high precision requirements. During the processing of shift shaft of transmission, through the simple installation and adjustment of some components of the fixture, the high efficiency and high precision of special fixture can be achieved with strong versatility, and the flexibility and variability of combined fixture can be achieved

gear shift shaft holes are generally processed by ordinary drilling machines, modular machine tools, machining centers and other equipment. Among them, modular machine tools have high production efficiency and are suitable for mass production, but the one-time investment of equipment is large, and the processing and adjustment time is long, which is not suitable for the production mode of multiple varieties and small and medium batches, and has great equipment investment risk, which is rarely used at present; The machine tool of machining center is easy to adjust and the process is relatively centralized, but the fixture design and manufacturing requirements are high, and the equipment investment is large, the relative cost of mass production is high, and the fixture adjustment of small batch production is cumbersome, so it is not widely used at present; Ordinary drilling machine equipment has small investment, high production efficiency and low requirements for operators' operating skills. Combined with different fixtures, it is suitable for mass, medium and small batch production of different types of enterprises, so it is widely used in the industry. Our factory has been using the common drilling machine since the 1960s

at present, the special fixture for miscellaneous parts of transmission suitable for batch method has achieved remarkable results after decades of exploration. In the increasingly fierce competition for new products, it is not suitable to use the traditional method for medium and small batch production and new product trial production. The main problems of the shift shaft drill fixture are as follows:

1 Special drilling fixture

(1) the waiting time of fixture is long (the design and manufacturing cycle generally takes 3 ~ 4 months)

(2) the demand for fixtures is large and the use cost is high (a set of fixtures are designed and manufactured in each process)

(3) high fixture manufacturing cost (more than 3000 yuan per set)

(4) as the product life cycle becomes shorter and shorter, the fixture elimination rate is high and the waste is large

(5) fixtures occupy a large amount of inventory and are inconvenient to manage

2. Combined drilling fixture

(1) fixture rental is frequent, rental cycle is long, and cost is high (the annual rental fee of shaft drilling fixture in our factory is up to about 30000 ~ 50000 yuan)

(2) the fixture is not rigid enough, the machining accuracy is unstable, and the product scrap rate is high

(3) there are many fixture components, and the assembly accuracy is low. Professional personnel are often required to adjust repeatedly in production, which wastes a lot of time

(4) the procurement cost of complete sets of fixtures is high

typical shift shaft drilling fixture

1 Typical structure of gear shift shaft drilling fixture

see Figure 1 for typical combined fixture and Figure 2 for traditional special fixture

Figure 1 Schematic diagram of typical combined fixture (slot positioning)

Figure 2 Schematic diagram of traditional special fixture (hole positioning)

2 The main characteristic dimensions and typical process routes of shift shaft products are shown in Figure 3. The number, position and angle of holes and grooves are variable

Figure 3 typical shift shaft drilling procedure

(2) typical product process route

process route is: blanking rough machining → rough and fine grinding excircle → milling multiple grooves → milling single groove → drilling straight holes → drilling inclined holes → hole chamfering → heat treatment and straightening → rough and fine grinding excircle → oiling and warehousing; The workpiece material is cold drawn round steel, with surface hardness less than hb285 and core hardness greater than hb179

(3) classification and grouping of product characteristic dimensions and accuracy (see Table 1) table 1 list of workpiece characteristic dimensions and accuracy

3 Fixture common problems

our factory produces dozens of light transmission shift shaft products all year round, and nearly 20 new products are trial produced every year. The structural elements, process elements and workpiece feature size elements of the products are similar, and the new products have good similarity and inheritance. Its drilling fixture has the following commonalities:

(1) the workpiece processing parts are similar, and the hole diameter and roughness are similar. Vertical drilling machines can be used to drill holes. By selecting different quick change drill sleeves (factory standard) and drills, the hole processing accuracy can be guaranteed

(2) the workpiece datum structure is similar, all of which are holes, grooves or shaft end face positioning, and V-shaped blocks, positioning shafts, angle plates and baffles can be used for positioning

(3) the tightening part of the workpiece is similar, which can be pressed on the pressing plate

(4) if the process elements of the workpiece are similar, similar elements can be positioned and clamped

(5) similar fixture structure can be adopted because the workpiece feature size and process elements are similar

4. The universal adjustable fixture scheme proposes that the universal adjustable fixture is composed of a universal matrix and replaceable components, which has good inheritance for the processing of products of the same family. When replacing similar processed parts, it can be put into production only by adjusting or replacing individual components. It has the characteristics of fast production and wide application. It is a modern machine tool fixture serving the processing of similar parts

in view of the above workpiece characteristic parameters and common problems, according to the workpiece similarity principle and size segment classification of the universal adjustable fixture, a set of universal adjustable fixture can realize the hole processing of our shift shaft series products

design scheme of universal adjustable fixture for gear shift shaft drilling

1 Design principle

(1) the fixture has rigidity, accuracy and service life that meet the process requirements

(2) the fixture structure is compact and concise, suitable for the same family products in the factory, and has room for expansion

(3) the fixture positioning element and the slot milling universal adjustable fixture designed at the same time can be borrowed from each other; The feature size of the positioning surface of the angle plate is similar to that of the combined fixture, which can meet the rental and substitution of components when necessary, and the overall design meets the requirements of low manufacturing cost

(4) the fixture guide element borrows the factory standard, which has strong interchangeability, and the positioning element design integrates standardized elements

(5) the fixture is convenient for installation, adjustment and measurement. It can replace the combined fixture and is suitable for the production of large, medium and small batches of products

2. General drawing of fixture structure

see Figure 4 for general drawing of fixture structure, figure 5 for p-direction positioning mechanism, and Figure 6 for positioning mechanism 2

Figure 4 general drawing of fixture structure

Figure 5 p-direction positioning mechanism

Figure 6 positioning mechanism 2

3 The main components of the fixture

(1) the general matrix of the fixture: 1 body, 1 drill template, 3 bushings and other standard components

(2) interchangeable parts of fixture: 2 V-shaped blocks and baffles respectively, 1 column support, 7 drill sleeves, 1 cushion block, 1 eccentric joint and pressing plate, 1 adjusting pad, 1 straight plate orientation plate, 1 bent plate orientation plate, 9 positioning shafts, 10 positioning pins, 5 angle plates, 1 positioning block, 6 directional keys and 3 positioning keys, etc. Other drill sleeves, directional keys, positioning keys and other components shall be selected according to the factory standard or national standard

4. Structural design of general matrix and key exchangeable components

(1) general matrix

drill template is firmly connected with the body through locating pins, equipped with drilling and reaming three holes of the template and installing bushings to ensure that the hole is 0.02 mm to the center of the V-shaped block

drilling three holes of the template is used to expand the drilling position and clamping space of different products. This method ensures that the key components of the fixture have the rigidity, accuracy and service life similar to the special fixture

(2) composite adjusting elements (V-shaped block, baffle, positioning block)

two different specifications of V-shaped blocks (suitable for shaft diameters below d16.3 and above D22) are connected with the T-shaped groove of the body through the positioning key, and sliding with the positioning block through the concave groove, and tightly connected with the baffle to form a composite adjusting element. The positioning error of this combined method is relatively small, and in the actual machining process, the clamping force and cutting force of the workpiece can offset each other, which can reduce the displacement error between components after being forced

during installation and adjustment, move the V-shaped block to ensure the distance between the concave groove center and the drilling template, or adjust the baffle set screw to ensure the distance between the shaft end face and the drilling template

(3) angle plate

installation method: select the angle plate and orientation plate according to the requirements of workpiece positioning angle, and connect them with the positioning block and orientation plate through the orientation key

working principle: slide or fix the orientation plate on the angle plate through the orientation key to ensure the angle requirements of the workpiece positioning groove or hole. Achieve positioning angle

(4) straight plate orientation plate

installation method: according to the positioning requirements of the workpiece groove or hole, select the positioning shaft or positioning column, and connect it with the positioning block or angle plate through the orientation key

working principle: fix or slide on the positioning block or angle plate through the directional plate to position the workpiece slot or hole. When positioning the groove, select the positioning column to meet seven positioning requirements; When positioning the hole, select the positioning axis to meet three positioning requirements

5. 11 fixture positioning modes

according to the different process positioning requirements of the workpiece, the ideal fixture mode can be achieved by changing the fixture angle plate and positioning block and moving the V-shaped block and pressing plate position. The fixture positioning mechanism can realize 11 positioning modes

(1) workpiece axial end face positioning (see Figure 7)

Figure 7 workpiece axial end face positioning

move the V-block and fine tune the baffle screw to ensure the distance from the shaft end face to the center of the drilling template hole. This positioning method is applicable to drilling the first non included angle hole

(2) horizontal positioning of workpiece groove (see Figure 8)

horizontal positioning of workpiece groove in Figure 8

move the V-shaped block to ensure the distance between the workpiece groove (or hole) and the center of the drilling template hole, and then push the positioning block to make the positioning pin closely contact with the workpiece groove (or hole), so as to realize the corresponding angle of drilling. It includes four positioning modes: upper positioning, lower positioning, angle positioning and hole positioning

(3) workpiece groove vertical positioning (see Figure 9)

Figure 9 workpiece groove vertical positioning

the method is the same as above, including six positioning methods of workpiece groove right side positioning, left side positioning, angle positioning, vertical hole positioning and angle hole positioning

6. Fixture installation and adjustment process

see Figure 10 for fixture installation and adjustment process

Figure 10 fixture installation and adjustment process

fixture accuracy analysis

1 Drill 2 with 205d transmission first and second shift fork shaft- φ Take 5 + 0.08 hole as an example, see Figure 11 for the process guidance diagram

Figure 11 process guidance figure

2 Fixture error analysis

take drill hole 2 as an example to analyze the hole spacing, perpendicularity, symmetry and included angle errors

(1) fixture manufacturing error (Manufacturing)

the manufacturing deviation between the center of the drill sleeve and the center of the V-shaped block is φ 0.02mm, the parallelism between the theoretical axis of the V-shaped block and the positioning datum plane of the body is 0.02mm; The angle manufacturing error of 10 ° angle plate is ± 2 '. That is, the center of the drill sleeve is in the radial direction of the workpiece axis: manufacturing =0.01mm; The center of the drill sleeve is in the vertical direction of the workpiece axis; Manufacturing =16.3 × 0.02 ÷ 271=0.0012mm (shaft section); Included angle between the center of the drill sleeve and the shaft groove of the workpiece shaft: manufacturing =2 '

(2) fixture installation error (installation)

during fixture installation, the development process of calibration from imitation to independent renovation is always unsatisfactory. The pin is introduced into the fixture by the drill jacket, and the drill jacket aligns the workpiece. The maximum offset between the center of the calibration pin and the center of the drill jacket is the fixture installation error, and the manufacturing deviation of the diameter of the calibration pin is φ 4.995 ~ 4.988mm, the drill sleeve adopts the factory standard, and the manufacturing deviation of the inner hole is φ 5.01~5.027mm ; Axial installation error of composite adjusting element is 0.02 mm; The comprehensive installation error of the 10 ° angle plate is about ± 2 ', that is, the center of the drill sleeve is in the radial direction of the workpiece axis: installation =0.0195mm; The center of the drill sleeve is in the axial direction of the workpiece shaft: installation =0.02mm; Included angle between the center of the drill sleeve and the shaft groove of the workpiece shaft: installation =2 '

(3) workpiece positioning error (positioning)

the V-block positioning reference coincides with the process reference; Effective stretching space interval of positioning error caused by workpiece straightness: 0 (7) 00mm, main equipment

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