Assembly and welding process and equipment selecti

D310 high top double sleeper cab assembly and welding process and equipment selection

D310 series cab has three series: one row and a half standard type, extended type and high top double sleeper type. The product R & D department requires that the "brim" on both sides of the cab be canceled to make the cab shape reach the level of Renault cab in France; The manufacturing department requires the cab bone accuracy to reach more than 85% and reach the quality level of Nissan Diesel G105 new cab; The cost management department requires a substantial reduction in investment to make D310 cab profitable; The production department requires that the three series of cabins of standard type, extended type and high roof double sleeper type are all produced in a mixed flow on a welding line

in order to eliminate the "brim" of the high top two bedroom cab, Renault Motor Company of France has adopted the exclusive and proprietary top cover block on-line assembly and welding technology, and the cab adopts advanced equipment such as flexible fixture assembly, robot welding, skid transportation, etc., with huge investment. We have neither the above technical data nor sufficient financial support, so the process design is very difficult, especially the high roof double sleeper cab. To this end, the company organized technicians to make bold innovations in the product segmentation, connection and positioning mode, assembly and welding process and equipment selection of D310 high roof double sleeper cab. With less investment, it realized the on-line assembly and welding technology of top cover segmentation, and produced a new cab with beautiful appearance, good quality and low cost

d310 cab assembly and welding process design began in October 2003, the D310 cab welding workshop was completed in December 2005, and the new commercial vehicle loaded with D310 cab began to be put on the market in May 2006

product assembly and welding process optimization

at the same time

1 Product description

d310 series cab outline drawing is shown in Figures 1, 2 and 3. The models are divided into three types: standard type, extended type, high roof double sleeper type, and the innovation ability and basic ability construction have been improved

Figure 1 outline drawing of standard cab

Figure 2 outline drawing of extended cab

Figure 3 outline drawing of high roof double sleeper cab

Figure 4 block diagram of D310 high roof double sleeper cab product

2 Selection of product segmentation and connection positioning mode

(1) product segmentation mode of high roof double sleeper cab

the top cover of Renault high roof double sleeper cab is divided into six parts: left, right, front, middle, rear upper and lower top covers. On the basis of keeping the cab top cover block assembly and welding on the line, we combined the rear upper top cover and the rear lower top cover into one piece, and successfully solved the problem of difficult welding of the rear top cover, reducing the workload and complexity of assembly and welding of the general assembly line. The optimized high roof double sleeper cab product block is shown in Figure 4

the assembly sequence of the high top double sleeper cab assembly is: floor assembly - left/right wall assembly - rear wall assembly - front top cover assembly, rear top cover assembly - middle top cover assembly - left/right door assembly

(2) connection mode of left/right top cover and left/right wall outer plate

the high roof double bedroom left/right top cover is assembled and welded on the left/right wall assembly instead, and the gutter at the connection between the left/right top cover and the left/right wall outer plate is cancelled, which meets the requirements of product appearance (as shown in Figure 5)

Figure 5 connection diagram of side top cover and side wall

(3) the connection mode between the front, middle, rear and left/right top covers

has been optimized for countless times. On the basis of meeting the requirements of product shape and structural strength, stamping and assembly and welding technology, mold and fixture manufacturing, the positions and dimensions of the lap edges of the high top front top cover, middle top cover, rear top cover, left/right top cover and 9 top cover reinforcing beams have been determined. In order to facilitate top cover welding, The skylight opening of the middle roof is retained, and the size of the skylight opening is determined

(4) assembly and positioning of the middle top cover assembly

in order to reduce the complexity and investment of the welding line, the middle top cover assembly adopts projection welding bolt positioning. Weld 1 M8 projection welding bolt at the left front corner and the right rear corner of the middle top cover assembly, and add 2 positioning holes (1 circular hole and 1 long hole) on the left/right top cover reinforcing beam accordingly. Just use a set of automatic on-line device to automatically transport the middle top cover assembly over the cab. The operators enter the cab and manually assemble M8 nuts and M8 bolts. The complex positioning fixture is eliminated, and the investment of the welding line is reduced

assembly and welding process design

1 Design conditions

production varieties: D310 one row and a half standard, extended, high roof double sleeper cab; Production program: 60000 sets/year; Production beat: 3.6min/set; Production mode: arbitrary mixed flow production

2. Process design idea

after the product design of D310 high roof double sleeper cab is completed, the selection of assembly and welding process and equipment is particularly important, which directly affects the production pace, product quality and process investment. Process design idea:

(1) standard, extended and high roof double sleeper cabins realize arbitrary mixed flow production on a welding line

(2) apply the top cover block on-line assembly and welding technology with less investment, and meet the requirements of product appearance and profitability at the same time

(3) reduce the level of welding automation and the number of robots

(4) adopt mature and reliable reciprocating rod conveying mode to replace the expensive high-precision skid conveying mode

(5) adopt mature and reliable traditional fixtures to replace expensive robot flexible fixtures

(6) adopt some manual positioning to replace the complex automatic positioning and reduce the complexity of the fixture

(7) some artificial pneumatic balancing devices are used to lift the assembly, replacing some automatic conveying devices

(8) adopt synchronous engineering technology, optimize product structure and process design, and shorten the project construction cycle

(9) improve the accuracy of cab bone to more than 85%

3. The process content and configuration of the general assembly line

the general assembly line can produce D310 one row and a half standard, extended and high roof double sleeper cabins at any mixed flow. There are 11 working positions, and the distance between stations is 5m. It is equipped with 1 set of reciprocating rod transmission line, 11 sets of welding fixtures, 3 sets of pre installed fixtures, 4 sets of spot welding robots, 17 sets of hanging spot welding machines, 3 sets of automatic conveying devices and 3 sets of manual conveying devices. There are 587 welding points in the general assembly line of the high roof double sleeper cab, including 317 robot welding points and 22 automatic welding machine welding points

one station: the general self-propelled hoist automatically places the floor assembly on the one station fixture

two stations: the left/right side wall automatic conveyor automatically assembles the left/right side wall assembly; Cantilever pneumatic balance crane is used to assemble the rear wall assembly; Automatic welding machine automatically spot weld 22 points; Two suspension spot welding machines spot weld 8 points

three stations: four suspension spot welding machines spot weld 87 points

four stations: two sets of automatic top cover conveying devices complete the conveying and assembly of high top front top cover assembly, rear top cover assembly and standard and extended middle top cover assembly respectively. Four suspension spot welding machines spot weld 21 points

five stations: two spot welding robots automatically spot weld 92 points

six stations: automatic assembly of automatic conveyor for high roof, middle roof and top cover. The leaders attending the meeting also included Meng Qingjun, Deputy Secretary General of China Plastics Processing Industry Association, Tian Yan, and Liu Shu, Deputy Secretary General of the cover assembly; Three suspension spot welding machines spot weld 36 points

seven stations: one general-purpose robot on the left automatically spot weld 68 points. A special robot for high roof on the right automatically spot welds 31 points

eight stations: one general-purpose robot on the right automatically spot welds 68 points. A special robot for high roof on the left automatically spot welds 58 points

nine stations: two hanging spot welding machines spot weld 96 points

ten stations: 2 sets of edge wrapping pliers are used to manually wrap the connection between the left/right wall and the rear wall

station 11: cantilever pneumatic balance hoisting with left/right door assembly

4. Improve the accuracy of cab bones

(1) unified product positioning datum

in the product design stage, the process positioning hole for assembly assembly is defined early, which is first proposed by the welding process, and then confirmed by the technicians in stamping process, mold manufacturing, fixture manufacturing and product design, and then marked on the product drawing to ensure the unification of the positioning datum of internal and external parts, molds, fixtures and inspection tools

(2) unified process positioning datum

68 sets of welding fixture positioning and clamping point layout drawings have been prepared. The fixture manufacturer designs according to the size and position of the positioning pin and positioning block proposed by the process, ensuring the unity of the positioning datum of sub assembly fixture, online fixture and inspection fixture

(3) ensure the quality of fixture design

the process has drawn the assembly welding spot drawing, the size drawing of manual welding tongs, and various detailed fixture design disclosure materials. The fixture manufacturer designs according to the requirements of the process, ensuring the quality of fixture design and manufacturing

(4) ensure fixture manufacturing quality

all online fixtures and sub assembly fixtures are measured and adjusted with CMM during pre acceptance and after on-site installation to ensure fixture manufacturing accuracy

(5) cab bone accuracy control

select more than 400 coordinate points on the cab for bone accuracy control. The management table and analysis and evaluation method of cab bone accuracy are compiled, so that the cab bone accuracy is steadily improved

equipment selection of final assembly line

1 The conveying equipment of left/right wall assembly and rear wall assembly is selected

D310 high top left/right wall assembly, which is large in volume, difficult to handle and assemble manually, and easy to deform, and is also limited by the height of the plant. Therefore, the left/right wall assembly is online by the combination of horizontal automatic lifting, transportation and overturning clamps; The rear wall assembly is lifted online by cantilever pneumatic balance crane. Manually lift the side wall assembly onto the pre assembly fixture - the pre assembly fixture moves horizontally - the automatic conveyor lifts the side wall assembly onto the turnover fixture - the fixture flips to the vertical state - the turnover fixture shifts to the assembly and welding position towards the center of the line - manually assemble the rear wall assembly - clamp the rear wall assembly - manual spot welding and automatic spot welding - automatically return to the original position after welding. Standard type, extended type, high roof double sleeper type left/right side assembly conveying equipment is common

the left/right side wall assembly adopts a 90 ° turnover fixture. Because the turnover fixture is very heavy, it needs 5T driving force. The electric driving mode is adopted, and the driving force is not enough; Pneumatic drive mode is adopted, with great impact. After repeated demonstration, the fixture turnover drive adopts the electric drive mode, but at the same time, it is equipped with a pneumatic balance power system, which effectively solves the difficult problem of fixture turnover

2. The conveying equipment of the front and rear top cover assemblies of the high roof and the standard and extended middle top cover assemblies is selected

D310. The front and rear top cover assemblies are large in volume, very difficult to handle manually and easy to deform. There is a negative angle when the front top cover assembly falls, which interferes with the left/right wall assembly. When the rear top cover assembly falls, it collides with the upper reinforcing beam of the rear wall assembly and cannot fall. After repeated demonstration, the front and rear top cover assemblies are transported by self hoist. The front and rear top cover assemblies are manually placed on the pre assembly fixture on the left side, and the self hoist transports the front and rear top cover assemblies from the pre assembly fixture on the line to the top cover assembly station. When the front and rear top cover assemblies are lowered close to the workpiece, the spreader will automatically push the lower part of the front and rear top cover assemblies forward and backward. When the front and rear top cover assemblies are lowered to the bottom, they will automatically return to the assembly position. The standard and extended middle cover assembly conveying equipment is arranged on the right side. The structure of the upper line device of the front and rear top cover assembly of the high roof double bedroom is shown in Figure 7. The positions of the positioning pins of the front and rear top cover assemblies of the high roof and the left/right top cover assemblies are shown in Figure 8

Figure 7 structure diagram of lifting appliance for front and rear top cover assembly of high roof

figure 8 adult positioning pins for front and rear top cover assembly of high roof and left/right top cover assembly