27-03-2014, 02:42 PM
SUMMER INTERNSHIP PROJECT AT MUNJAL SHOWA LTD
EXECUTIVE SUMMARY
Munjal Showa Company is in the business of making suspensions for Hero Honda, Maruti and Honda. Most of the production is of two wheeler suspension. The project given to me was on bottom case line and 4W piston rod line. The Pareto analysis showed that the major problem occurring in the bottom case line of fender up and down during milling process. The major problem in the piston rod line was grooving problem.
The data available in the company showed that the fender up-down problem existed for many years but the grooving problem was new to the company and the rejection level is increasing every month.
On interviewing operators and analysing the samples, I found the causes of the problems. The major causes of the milling problem were related to machine only. The cutter used was not of accurate design. The clamp and the guide pin were not as per the design parameters. The cause of grooving problem was stopper length. The stopper got eroded after prolonged operations. So the rejections were continuously increasing.
A new cutter, a clamp and a guide pin were made and trail was done. For solving the grooving problem, a new stopper of accurate length was made and an additional carbide tip was put to the stopper face to prevent erosion. The test results were favourable and consistent. Groove length of 4w rod swift rear model (43.0-43.4 mm) under control. S.D reduced from 0.097 to 0.035. Fender parallelism under control (within 0.3 mm). Left B.C parallelism range: (0.13-0.25 mm). Right B.C parallelism range: (o.11-0.24 mm)
PROBLEM DEFINITION
GROOVE LENGTH PROBLEM
There is a variation in the groove length during grooving process in 4w piston rod of swift rear model. The problem belongs to category B problem (inline process problem). The inline process problem means the problem has occurred due to fault in the machining process. This deviation in groove length causes change in final length of suspension, which does not fit.
FENDER UP DOWN PROBLEM
There is a variation in the fender parallelism in front and rear bottom case of 2w during milling process. The Maximum permissible variation allowed is 0.3mm. The problem belongs to category B problem. It causes misalignment of suspension. Due to this misalignment, the suspension creates noise and oil too gets leak from it.
WIKIPEDIA: Spring rate
The spring rate (or suspension rate) is a component in setting the vehicle's ride height or its location in the suspension stroke. Vehicles which carry heavy loads will often have heavier springs to compensate for the additional weight that would otherwise collapse a vehicle to the bottom of its travel (stroke). Heavier springs are also used in performance applications where the loading conditions experienced are more extreme.
Springs that are too hard or too soft cause the suspension to become ineffective because they fail to properly isolate the vehicle from the road. Vehicles that commonly experience suspension loads heavier than normal have heavy or hard springs with a spring rate close to the upper limit for that vehicle's weight. This allows the vehicle to perform properly under a heavy load when control is limited by the inertia of the load. Riding in an empty truck used for carrying loads can be uncomfortable for passengers because of its high spring rate relative to the weight of the vehicle. A race car would also be described as having heavy springs and would also be uncomfortably bumpy. However, even though we say they both have heavy springs, the actual spring rates for a 2,000 lb (910 kg) race car and a 10,000 lb (4,500 kg) truck are very different. A luxury car, taxi, or passenger bus would be described as having soft springs. Vehicles with worn out or damaged springs ride lower to the ground which reduces the overall amount of compression available to the suspension and increases the amount of body lean. Performance vehicles can sometimes have spring rate requirements other than vehicle weight and load.
Wheel rate
Wheel rate is the effective spring rate when measured at the wheel. This is as opposed to simply measuring the spring rate alone.
Wheel rate is usually equal to or considerably less than the spring rate. Commonly, springs are mounted on control arms, swing arms or some other pivoting suspension member. Consider the example above where the spring rate was calculated to be 500 lbs/inch, if you were to move the wheel 1 in (2.5 cm) (without moving the car), the spring more than likely compresses a smaller amount. Lets assume the spring moved 0.75 in (19 mm), the lever arm ratio would be 0.75:1. The wheel rate is calculated by taking the square of the ratio (0.5625) times the spring rate. Squaring the ratio is because the ratio has two effects on the wheel rate. The ratio applies to both the force and distance traveled.
Wheel rate on independent suspension is fairly straight-forward. However, special consideration must be taken with some non-independent suspension designs. Take the case of the straight axle. When viewed from the front or rear, the wheel rate can be measured by the means above. Yet because the wheels are not independent, when viewed from the side under acceleration or braking the pivot point is at infinity (because both wheels have moved) and the spring is directly inline with the wheel contact patch. The result is often that the effective wheel rate under cornering is different from what it is under acceleration and braking. This variation in wheel rate may be minimized by locating the spring as close to the wheel as possible.The suspension parts includeprings,shock absorbers, arms, rods, ball joints, axels, wheels and tyres. these suspend the body and associated parts so that they are insulated from road schocks and vibrations which would otherwise be transferred to the passengers and load. parts of front suspension also perform steering function
CONCLUSIONS
Groove length of 4w rod swift rear model (43.0-43.4 mm) under control.
S.D reduced from 0.097 to 0.035
Fender parallelism under control (within 0.3 mm)
Left B.C parallelism range: (0.13-0.25 mm)
Right B.C parallelism range: (o.11-0.24 mm)
Trail results were favorable and consistent
Able to reduce the milling rejections by 27 pieces/day
Able to almost eliminate the grooving problem in swift rear rod