(1) Design troubles in LCA designs

The LCA automation systems and fixtures are mostly fastened by the use of screws (incl. nuts and bolts). Therefore, designing with screws affect the following items.

Therefore, screw designing cannot be overlooked for the LCA designs that are lean and functional.

(2) Screw troubles during designing and post implementation

Screw troubles during designing and after the implementation can be classified as two of the following.

(a) Troubles arising LCA assembly and fastening ---- When there are LCA design errors

-Example

1. Correct bolts to fit the counterbore holes and thread depths are not in stock
2. Screw position is not aligned with mating threads.
3. Damaged threads during assembly.
4. Part is deformed from tightening force.

(b) Troubles arising when time has past after fastening ---- Errors in strength evaluation during designing.

-Example

1. Screws coming loose causing the parts to be misaligned causing equipment damages.
2. Destruction of bolts
   Both a) and b) are caused by the designer's ineptitude during designing.

Explanations on assembly datum features that are easy to machine

a) Obtaining datum accuracies

• Choose accurate machine tools in order to accurately machine the parts with assembly datum features.

↓

Utilize the inherent positioning accuracy characteristics of accurate machine tools to obtain high accuracies of the parts with assembly datum features.

-Explanation
Machine tools use precision guides for accurate motion and precision measurement instruments for accurate positional detection to move the cutting tools in desired manner to obtain the targeted shapes accurately. For this reason, the machines that produce highly precise parts are called "Mother machines"

-Examples
Hole position accuracy: ±0.5mm > Drill press
Hole position accuracy: ±0.01mm > CNC Milling machine
Hole position accuracy: ±0.005mm > Jig boring machine
Datum plane accuracy: ±0.01mm > CNC Milling machine
Datum plane accuracy: ±0.005mm > Precision flat grinder

b) Easy machine assembly datum designs

• Utilize the inherent accuracy of the machine tools for parts accuracy.
• Use the external profile (or datum reference holes) features as the datum surfaces, and measure from these surfaces to machine the assembly datum features. (2 red lines show in Fig. are the datum lines)
• Therefore, an easy to machine design is where all the datum locations can be machined at once while the part is mounted on a machining fixture.
• If a fixtured part must be unfixtured and reset (ex. reversing), resetting error will result.

↓

Highly accurate and cost effective part designs are where the parts' all datum features can be machined at once with one time fixturing.

Question

Let us design the side gate at one location in the case of an injection molded article made of Polyacetal (POM) plastic, when the average wall thickness of the molded article is 1.5 mm and the surface area of the molded article is 4900 mm²,
In this case, obtain the guidelines for the design dimensions of the gate depth h and width W.

Sample Answer

The side gate dimensions are determined in the following two steps.

First Step: Determining the gate depth

First, we check the wall thickness t (mm) of the molded item.
From the question, we find that t = 1.5 (mm).

Next, we obtain the coefficient n which depends on the molding material from Table 1.
In the case of Polyacetal, n = 0.7.

Therefore, the depth h of the side gate will be:

h = n ∙ t
= 0.7 x 1.5
= 1.05 (mm)

Second Step: Determining the gate width

First we obtain the surface area A (mm²) of the molded item.
From the question we find that A = 4900 (mm²).

Next, we obtain the coefficient n which depends on the molding material from Table 1.
In the case of Polyacetal, n = 0.7.

Therefore, the width W of the side gate will be:

W = n ∙ √A/30
= 0.7 x √(4900) /30
= 1.63 (mm)

In conclusion, considering the ease of machining the mold and its cost, we determine as follows:

h = 1 (mm)
W = 1.6 (mm)

The side gate dimensions are determined in the following two steps.

First Step: Determining the gate depth

First check the wall thickness t (mm) of the molded article.
Next, obtain the plastic resin dependent coefficient n from Table 1.

Table 1

Next, obtain the depth h (mm) of the side gate using the following equation.

h = n ∙ t

Second Step: Determining the gate width

First obtain the surface area A (mm²) of the molded item.
Next, obtain the molding material dependent coefficient n from Table 1.
Finally, obtain the gate width W (mm) from the following equation.

W = n ∙ √A/30

Fig. 2 shows the progressive blanking operation. In progressive blanking, the blanking is done successively while moving the material which is kept connected by the bridge part. The "bridge" in this case is not important for the blanking operation but is mainly intended to hold the blank in a stable manner, and to feed the blank to the next process. Therefore, in order to distinguish this from the blanking bridges, most often such "bridges" are called "carriers" in progressive blanking. The three types of carriers shown in Fig. 2 are the double side carrier, the single side carrier, and the center carrier. The double side carrier holds the blank in a stable manner. Depending on the method of using, the instability remains in the cases of the single side carrier and the center carrier.

Although in general the part of the material that connects the blanks is called a "bridge", depending on the application, if the method of using is mistaken, there will be abnormalities in the product quality. Do not make simple judgments merely based on the way it is called.

(2) Blank holder (Fig. 2)

(3) Pressure pad (Fig. 3)

As can be understood from the respective figures, the structures are all the same. They are called by different names only depending on their purpose of use. The name indicates what is expected of the part.

In actual process work sites, experience based tests such as water drop tests and water draining tests. These tests are used since they are simple, easy, and can be performed in short amounts of time as they are quite pragmatic for the work sites. There are various cleanliness tests being performed in various process scenes as shown below.

(1) Visual inspections

Visually compare the specimen against prepared reference sample for surface stains and oxidation film.

(2) Wiping tests

Metal surfaces are wiped off with tissue paper, filter paper, or white cloth and check the soiling substance wiped off. Although it's a simple method, this is effective in detecting some minute particles missed by other tests. In comparing wet and dry surfaces, it is more likely to detect the minute particles on wet surfaces. However, the wiping pressure applied is important where relatively high pressure will be required to detect the substance called "smut' that may exist on cold rolled steel after an acid pickling process.

(3) Water wetting test

This test utilizes the hydrophilic surface nature where the surface will retain water when no oil exists. Since it only involves wetting the sample with water, it is a simple and non-destructive test used widely. Notes on this test are: (1) water used is to be clean and cold (warm water should not be used since evaporates quickly and promotes rusting), (2) The sensitivity of this test will depend on the water film thickness. Thinner the film, the higher the test sensitivity.

Detail explanation is given below.

4) Spray pattern test
5) Atomizer test
6) Fluorescence test
7) Contact angle test
8) Radioactive tracer test
9) Rusting test
10) Plating test
11) Wear coefficient measurement method
12) Contact electrical differential test
13) Others

[Fig.1] Shows the principle of reverse osmosis.

When pure water and salt water placed in a tank divided with a semi-permeable membrane (a membrane with extremely fine size holes on the surface), the pure water permeates the membrane and enters the salt water side of the tank, diluting the salt water. This is called Osmosis. The energy for this is called Osmotic Pressure, and depends on the concentration of the salt water. If the diameter of the membrane's holes is larger than the diameter of the salt molecules, the salt will migrate to the pure water side until both tanks are of the equal concentration level. This would be called Divergence.

As shown in [Fig.1] above, pressurizing the salt water using a membrane with very fine holes, only the water of the salt water solution migrates to the water side. This is called Reverse Osmosis. In actual application, a tubular formed semi-permeable membrane (for improved pressure resistance) is used. Filtered water and concentrated water are obtained when precision filtered water is pump pressurized and sent through the tube.

[Fig.3] shows a water purification system with a reverse osmosis module integrated

(1) Relative positions between belt support brackets and conveyor

In case of the work transfer conveyor shown as an example, work piece takes the following three types of actions on the conveyor belt at the three locations. At each location, a non-contact sensor monitors the presence or absence of work pieces to control the operation of the conveyor belt. Therefore, the conveyor belt needs support from underneath with the belt support to specifically stabilize the positions of the work pieces at the sensor locations (See Fig. 1):

1. Placement
2. Positioning
3. Pre-ejection pause

(2) Belt support brackets shaped for easy adjustment

Functionally, the work transfer conveyor does not require precise parallel alignment between the top side of the conveyor belt and the base plate. Accordingly, the belt support bracket shapes are preferably designed under the assumption that the assembly will not be parallel. Additionally, there should be three separate belt support brackets to stabilize the three types of positions explained in (1) above, and each bracket should be designed to consist of two parts to allow height adjustment (see Fig. 2):

(3) Designing belt support brackets at low cost

The design cost should be minimized from the following points of view:

(1) Reduction in number of parts

Reduction in the number of parts is advantageous and minimizes manufacturing costs. For functional reasons, however, the number of belt support brackets is set at three. Hence, the three brackets should have identical shapes to minimize design and machining costs.

(2) Reduction of manufacturing cost

Parts manufacturing cost is divided into the material cost and machining cost to develop a low cost design.

- Part manufacturing cost minimization

Select a commercially available standard material that requires minimal outside machining. Two-millimeter thick cold-rolled steel sheets (JIS SPCC) are selected on the basis of the weight of the conveyed work pieces. SPCC sheets characteristically excel in dimensional accuracy, surface smoothness, and the workability properties of bending, drawing, cutting, and welding.

- Machining cost minimization

Machining cost minimization means reducing the time required for machining. This is almost synonymous with minimizing the amount of material removed. The bracket structure selected here is weld-reinforced for strength and requires no machining except for the drilling position adjustment holes (see Fig. 3):

An "insert block structure" is one in which the core is divided at the undercut part, the divided core (insert block) is taken out along with pushing out the molded product, and after that, the insert block is removed by hand.
At the time of the next molding, the insert block is set inside the mold again.
Therefore, in the case of an insert block structure there is the drawback that the molded product becomes a semi-automatically prepared item.
However, since it is possible to provide the desired undercut shape in the integrally molded product, this is a very useful method in special cases when such special structures are required.

In summary, the molded product in which the advantages of the insert block structure are brought out are the following.

1. Molded product in which it is not possible to handle undercuts using the ordinary slide cores, etc.
2. Molded product having undercut shapes, but whose production volume is small.
3. Sample molded product

Since an insert block is installed and removed manually, techniques such as machining or chamfering the escape for guiding the block inserting part, and the mating tolerances will be the know how of the manufacturer.

It is not always necessary that molds must have structures suitable for automatic production, and for designers in the digital age it is very important to know that it is possible to obtain the desired molded product by incorporating manual steps that are more analog than digital.

The conventional plastic resin synthesized by petroleum chemistry cannot be dissociated by bacteria, and are considered to remain permanently as waste. However, due to the recent advances in chemical technology, plastic resin materials have been developed that are dissociated into water and carbon dioxide. Some of such materials have already been made into commercial products and are being used in various injection molded items.

After using the molded items produced from a biodegradable plastic resin, they are buried underground, or are mixed with kitchen garbage as compost and left to decompose. These are ideal materials for preserving the earth's environment and for preventing global warming.

In order to use biodegradable plastics resin in industrial products or as packaging materials, while it is necessary that they have a certain strength and heat resistance, and satisfy the standards related to food and hygiene, products satisfying these requirements are being successfully commercialized one after the other.

The tableware used in the restaurant in the Aichi World Expo held in March of 2005 were made of biodegradable plastics, and this fact was clearly stated in the administrative policy speech by the then Prime Minister Koizumi during the normal Diet session held in February 2005.

It is considered that the practical realization of biodegradable plastics resin will progress at a very fast pace in the fields of electrical home appliances, interior decoration parts of automobiles, tableware etc, and in various other fields in about three years from now.

Some of the major biodegradable plastic materials are described below.

■ Poly-lactic acid (PLA)

This is a plastic resin that is synthesized only from starch produced from corn or potatoes, and is a material whose commercialization has progressed most.
Grades have appeared that can improve the heat resistance and strength, and are being used practically in parts of electrical home appliances, computer products, returnable food containers (bowls, cups, etc. that can be used in dish washers).
In the case of heat resistant grades, although problems have been pointed out that it is necessary to maintain the mold temperature at 110 to 120°C, and that separating from the mold is very difficult, production methods have been developed to solve these problems.

■ Poly butylene succinate (PBS)

This is a biodegradable plastic resin made from soft biomass of which succinic acid is a typical constituent. While poly-lactic acid is suitable for high hardness molded items, PBS is suitable for soft molded items.

■ Poly vinyl alcohol (PVA)

■ Poly glycolic acid

Fig. 1 shows the relationship between the plate thickness and the diameter of the dowel pin. In general, there is a correlation between the plate thickness and the area, and it is assumed that a plate with a large end surface relative to the thickness is not used.

Fig. 2 and Fig. 3 show the dimensions from the end surface of the plate or block taking the dowel pin size as the reference. Although a dowel pin diameter of 12 mm has been shown in the table, there are dowel pins with a diameter of 13 mm also. These dowel pin diameters of 12 mm and 13 mm are created from the standard value of 12.5 mm. Which one of the two diameters to use is up to the liking of the user. Although recently the use of 13 mm is increasing, it is possible to use either of these two diameters.

(1) Secondary electrolytic tin as lubricant

An alumite film formed with a sulfuric acid bath and then subjected to a secondary electrolytic tin bath will have an extremely low wear coefficient. Table 1 shows the results of such a test. As is clear from the table, the films with only their pores filled with tin showed increases in the wear coefficient proportional to the number of times the pores experienced friction. Meanwhile, the film with pores over deposited with tin showed a constant wear coefficient. Thus, an anodic oxide film formed on the aluminum, a relatively soft metal, and further coated with a thin film of soft metal such as tin or cadmium provides wear resistance under low loads.

[Table 1] Wear coefficients of tin-deposited films *

*Load of 99 g, steel ball diameter of 5 mm, stroke of 10 mm, and speed of 3.9 mm/sec

(2) Secondary electrolytic deposition of MoS₂

An anodic oxide film subjected to a secondary electrolytic bath consisting mainly of ammonium molybdate is provided with pores filled with directly produced highly lubricating molybdenum disulfide (MoS₂).

(3) Electrophoretic Teflon particles

When immersed in a solution containing dispersed particles (0.5 to 5 μm) of Teflon (tetrafluoroethylene) recognized for excellent lubricity and non-adhesiveness (resistance to adhesion), an anodic oxide film-covered work piece will become an anode for electrophoresis so that the pores in the alumite will be filled with negatively charged Teflon particles. This technique is well known as the Tufram process.

(4) Wear coefficients of anodic oxide films

Fig. 1 is a summary of the wear coefficients of the anodic oxide films described above: