[Table.1] Relationship of LCA design and LCA cost reduction

The LCA design process begins with a conceptualizing of functions with illustrations, then proceeds to design drawing and manufacturing drawing creations. To this point is a process of turning the abstract ideas into drawing information.
After the drawings are created, parts are manufactured and purchased components are procured according to the drawings, then on to assembly work and programming. All of these steps are executed according to the contents of the design. Therefore, it can be said that a good LCA depends on a good design.
A manufacturing system including LCAs are composed of purchased parts such as screws and springs, purchased machine elements such as motors, etc., and machined components made of raw materials (including control programs). Cost reduction ideas for each, as well as assembly/maintenance cost reduction ideas can be summarized in a table above. It can also be seen from this table that the quality of design largely affects the success rate of LCA.

We'll begin with sorting of the design process and a flow. [see Fig. 1] "Designing" is a process of decision making (on LCA performance, manufacturing drawings, and information on how to operate) to create "Something" when a need to materialize such "Something" arises. If the design process is commenced forward without giving the proper thoughts, separate design drawings would be need for every production item and the amount of work required will increase exponentially. In actuality, businesses are offering wider variety of products.

For this diversifying needs, there is a design approach called VR (Variety Reduction)

[Table] VR Design Approach

Explanatory diagrams of the examples of four types are shown in Fig. 1.

A. Bolt connecting

Bolt connecting is the method used frequently in large molds in which there is enough space to provide screw holes and bolt fixing holes in the cavity and the core. It is possible to fasten strongly because of the screw. It is possible to consider the method of tightening the bold from the parting surface side or the method of bolt tightening from the side of the mold plate back surface. The direction of bolt tightening is selected suitably depending on the conditions.
For the screw, usually metric coarse thread is used.

B. Flange retaining

Flange retaining is the method used when sufficient space is not available for provided screw holes and bolt fixing holes in the cavity and core.
Usually, the two methods of double side flange and single side flange are used. The amount of catching by the flange is about 1 to 2mm, and the height of the flange is about 3 to 10mm, and the selection is made depending on the size of the core.

C. Key retaining

Key retaining is the method used when fastening several components in which case it is difficult to use the flange retaining or the bolt fastening methods.
The shape of the key can be that of the bracket character "]", straight key, round key, etc.
It is necessary to consider the dimensions of key mating.

D. Press fitting

Press fitting is a mold fastening method that is used very frequently in the case of large molds. The external dimensions of the cavity and core are machined so that they fit tightly in the pocket carved from the parting surface side, and the press fitting is made by hitting with a plastic hammer, etc.
If this method is used, since the dismantling of the cavity and core becomes difficult at the time of maintenance, sometimes a hitting hole is provided in the bottom surface of the pocket for dismantling.

Fig. 1 Cavity and core integrated structure and divided structure

（Evaluation: = Excellent,　= Good,　= Partially satisfactory,　= Not suitable.）

Comparison item Integrated structure Divided structure Component count Ease of machining - - Cost of machining - - Material cost Corner part shape accuracy Ease of polishing Air vent effect Ease of maintenance

The decision of whether to use an integrated structure or a Spliting structure should be made considering the shape of the molded product, the life of the mold, the type of plastic, etc., after weighing the pros and cons. We are frequently asked which structure is good, and our answer is that which type is good or bad is determined based on the preconditions for selection.

The slide of the press machine starts moving down from the top dead center (0° ) and reaches the bottom dead center (180° ). Material feed is started from the mid point (270° ) of the return process, and completes the feeding at the mid point (90° ) of the lowering process (typical timing). The feeding device not only does this kind of simple movement, but also carries out a little more complex movement.

Some feeding error occurs during material feeding. This feeding error does not become a problem if it is a product that is finished in one stroke such as a blanking operation. However, during successive forming, a product gets completed only after several strokes. In such forming, feed errors are not permissible and corrections become necessary. This role is played in a mold by a pilot. A pilot moves the material finely by entering into the pilot holes made in the material thereby correcting the feed errors. If the feeding device is clamping the material at this time, the pilot cannot move the material and correct the error.
It is necessary that the feeding device releases the material at timings matching with the movement of the pilot. This movement is called "material releasing". Usually, material releasing is matched with the position at which the material is lifted in the die (material lifting position). The end of material releasing (material clamping) is done after the slide has passed the bottom dead center.

There are two typical forms of material feeding devices, namely, roll feeder and gripper feeder.

Fig. 2 shows the principles of operation of a roll feeder.

This feeder is made up of a top roller and a bottom roller. The rollers feed the material by intermittently rotating by a distance equal to the feed length.
Unidirectional clutches, various types of cam mechanisms, and servo motors, etc., are used as the means for carrying out intermittent rotation.
Usually, the bottom roller is fixed, and the top roller is pressing against the bottom roller by the force of a spring, etc. For material releasing, the top roller is pushed up using a lever, etc.

Fig. 3 shows the principles of operation of a gripper feeder.

This feeder has two clamps, namely, a feeding clamp and a fixed clamp. As can be understood from the figure, the feeding clamp repeats the operations of opening >> returning >> closing >> feeding. The fixed clamp goes into the open state when the feeding clamp is carrying out the feeding operation and will be in the closed state during all other operations of the feeding clamp. Next, at the time of material releasing, both the feeding clamp and the fixed clamp carry out the opening and closing operation simultaneously.
The movements of the gripper feeder can be operated using air by switching some valves, or can be carried out using some mechanisms such as cams, etc.
During the operations of material feeding, the position of releasing the material changes depending on the amount of material lift. It is necessary to adjust the timing of releasing to match with those changes.

The structure of this type is simple and this type is used widely because it is easy to manufacture. There is a form called eccentric shaft among crank shafts, but recently there is no particular preference being given to any shape of the shaft (because the completeness of the press machine becomes high and since it is possible to confirm that the required functions are being satisfied by checking the specifications).

Another typical mechanism is the knuckle mechanism in a press machine. This type of structure is shown in Fig. 2. This is a machine in which the slide is being driven by adding a link to the crank mechanism.

The reason why press machines are manufactured by changing the mechanism is the stroke curve shown in Fig. 3.

In a crank press, as soon as the slide reaches the bottom dead center, the returning step is stared immediately. In press forming, if there is a slight pressing time at the bottom dead center, there is the characteristic that the formed shape becomes stable. Modifications are made to the drive mechanism in order to exploit this characteristic. The stroke curve of the knuckle mechanism in Fig. 3 becomes more gradual near the bottom dead center compared the stroke curve of the crank mechanism, from which it can be seen that the pressing time is longer than in the case of the crank press. It can be said that this mechanism is one that was prepared for obtaining this forming curve.

Because of this characteristic of the knuckle press is used frequently in the case of forming that includes crushing or when countermeasures are to be taken against spring back of bending, etc. Its disadvantages are that it is difficult to prepare long strokes, and that, since the number of joints becomes large, the overall gap is likely to become large, etc. However, high precision modified press machines of this type are being manufactured at present.

Apart from the above, there is also a type called link press. This type is prepared with the intention of obtaining gradual movement at the bottom dead center and fast returning. In addition, by changing the mechanical details, there are machines in which changes have been made in the motor. This type is called a servo motor press. The press machine of the mechanical type assumes a constant rotation of the crank shaft within one stroke. If it is possible to change the rotation of the shaft, it will be possible to prepare any stroke curve freely. Perhaps the manufacturing of molds may become somewhat easier.

A representative example of Nonuniform Environment Corrosion is a case for bulkhead steel plates for shoreline protection. The waterline areas of these steel plates are severely corroded whereas the other parts of the plates are not. This is because the waterline areas are submerged during the high tides, and exposed to the air during the low tides. It can be said that the waterline areas and the other areas of the steel plates are subjected to nonuniform corrosive environments. In water, the differences in dissolved oxygen levels cause localized corrosion.

Localized corrosion also causes holes. A small opening diameter but deep corrosion is called "Pitting". For carbon steels, wide opening but shallow "dish or mortar shaped" corrosion occur often. For passive surfaced metals such as stainless steel, pitting occurs. The reason for that is thought to be the following. Passivated metals have several nanometers thick of highly corrosion resistant passive layer on the surface, and normally do not corrode in air and water. But if enough chlorine ions exist in the environment (i.e. sea water) this passive layer can be broken and nonuniform conditions will promote the advancing of the corrosion, thus pitting occurring.

Let us think about metal corrosion in some general terms. Suppose We throw a piece of Polished metal in a corrosive environment. Depending on the metal type and the corrosive environment, the following changes would occur on the metal surface.

(1) No change on the surface

This means that no byproduct of corrosion was formed on the metal surface, or the surface deposits were in nanometer order thin, and the corrosion would not advance any further.

(2) Discolors but no further change

The corrosion byproduct has grown to become visible to the eyes, covering the surface densely but the corrosion will not progress further. The discoloration is of tens of nanometer thickness.

(3) Rough rusts are generated and the corrosion advances

The corrosion byproducts do not adhere tightly to the surface, causing the surface to be constantly exposed to the corrosion causing environment promoting the corrosion progress. The generated rust flakes off. This is the corrosion symptom for mild steel objects exposed to outdoor rain and wind. For coastal areas, salts would cause more severe rusts.

(4) No rusts evident but the corrosion advances

When the corrosion byproducts dissolve into the environment, the rust will not be visible but the corrosion will continue to progress and the metal will continue to be depleted. This is the case of metals in acids.

As seen above, there are different types of corrosion progression. Corrosion types can be categorized into:General Corrosion where the corrosion occurs on the full surface uniformly, and Local Corrosion where corrosion occurs in regional concentrations.
However, in a strict aspect, uniform corrosion cannot occur unless the Metal composition and structure are uniform and the environment is also uniformly corrosive. In reality, some localization of corrosion is occurring.

Corrosion of steel in water or high temperature high temperature gases occur almost uniformly, and are called General Corrosion, in an approximation term. The index used to indicate the magnitude of uniform corrosion are "Corrosivity" 25mg/dm²/day (25mg of corrosion per 1dm² per day, and 0.12mm/y (0.12mm thick corrosion per year).