> Selective Laser Sintering (SLS) is an additive manufacturing process that utilizes a high-powered laser to selectively fuse powdered materials, such as thermoplastics or metal powders, to create three-dimensional objects layer by layer.

## The SLS process involves the following steps:

1. An even layer of powdered material, such as nylon or metal, is spread across the build platform.
2. A high-powered laser scans the digital model's cross-section onto the powdered bed, selectively sintering or fusing the powder particles according to the model's specifications.
3. After each layer is scanned and sintered, a new layer of fresh powder is applied, and the process repeats. The build platform gradually moves downward, and the laser continues to sinter each layer until the object is complete.
4. The finished object cools down within the powder bed to maintain its shape and structural integrity.
5. The printed object is carefully extracted from the powder bed. Excess powder is cleaned off, and the remaining powder can be reused, minimizing material waste.
6. Additional steps, such as support structure removal, surface finishing, or polishing, may be performed based on the desired outcome.

## Advantages of SLS include:

1. **Material Versatility:** SLS can work with various materials, including plastics, metals, ceramics, and composites, expanding its potential applications.
2. **Support-Free Printing:** The unsintered powder acts as its own support, eliminating the need for additional support structures during the printing process.
3. **Complex Geometries:** SLS can produce objects with intricate designs, internal cavities, undercuts, and complex geometries, without requiring assembly.
4. **High Strength and Durability:** SLS prints often exhibit excellent mechanical properties, making them suitable for functional parts and end-use applications.
5. **Material Reusability:** The unsintered powder can be reused in subsequent printing jobs, reducing material waste and cost.

## Disadvantages of SLS include:

1. **Post-Processing Requirements:** Additional steps, such as removing excess powder, may be necessary to achieve the desired surface finish.
2. **Resolution Limitations:** SLS may have constraints in achieving high levels of detail and surface smoothness compared to other additive manufacturing processes.
3. **Equipment Cost:** SLS machines and the required high-powered lasers can be expensive, making it more suitable for industrial applications.

## Applications of SLS encompass various industries:

1. **Functional Prototypes:** SLS is widely used for creating functional prototypes in automotive, aerospace, and consumer goods industries.
2. **End-Use Parts:** SLS is suitable for manufacturing customized and low-volume production parts, particularly when strength and durability are crucial.
3. **Tooling and Jigs:** SLS produces tooling components like molds and jigs for various manufacturing processes.
4. **Medical Applications:** SLS finds use in producing patient-specific implants, surgical guides, and anatomical models in the medical field.
5. **Complex Geometries:** SLS enables the production of intricate architectural models, artistic sculptures, and complex designs that are challenging to achieve using traditional manufacturing methods.

Selective Laser Sintering (SLS) expands the capabilities of additive manufacturing by offering material versatility, complex geometry production, and the ability to create functional prototypes and end-use parts with high strength and durability. It finds applications across industries such as automotive, aerospace, medical, and art.

Selective Laser Sintering (SLS): Advancing Additive Manufacturing Capabilities


> Stereolithography (SLA) is an additive manufacturing process that utilizes a liquid photopolymer resin to create intricate and precise three-dimensional objects. By selectively curing and solidifying the resin layer by layer using a focused UV laser, SLA achieves exceptional detail and surface finish.

## The SLA Process:

1. A digital 3D model is created using CAD software, and it is saved in STL format, which is compatible with SLA printers.
2. Slicing software is utilized to divide the 3D model into thin, horizontal layers, generating instructions for the SLA printer.
3. A liquid photopolymer resin is chosen based on the desired properties, such as mechanical strength, transparency, flexibility, or heat resistance.
4. The SLA printer's vat is filled with the selected resin, ensuring proper positioning of the build platform.
5. The build platform is lowered into the resin, and a focused UV laser selectively cures the first layer based on the sliced data.
6. The build platform gradually rises, separating the cured layer and allowing the resin to flow back for the next layer.
7. The SLA printer continuously scans and cures each subsequent layer, incrementally raising the build platform until the object is fully formed.
8. Once the printing is complete, the object is carefully removed from the vat and rinsed in a solvent bath to remove excess uncured resin.
9. To achieve the final strength and material properties, the printed object undergoes post-curing using UV light or a specific curing chamber.
10. Additional steps, such as removing support structures, refining surface finish, or applying coatings, can be performed if needed.

## Advantages of SLA:

1. **High Resolution:** SLA delivers exceptional detail and surface finish, suitable for intricate and visually appealing objects.
2. **Material Choices:** Choose from a wide range of photopolymer resins with different mechanical properties and characteristics.
3. **Smooth Surface Finish:** SLA prints have minimal visible layer lines, resulting in polished and smooth surfaces.
4. **Accuracy and Precision:** SLA offers high dimensional accuracy, making it ideal for applications with tight tolerances.
5. **Support Structures:** SLA printers generate easily removable support structures for complex geometries.

## Disadvantages of SLA:

1. **Limited Print Size:** SLA printers typically have a smaller build volume compared to other 3D printing technologies.
2. **Post-Curing Process:** Objects printed with SLA require additional time for post-curing to achieve their final strength and stability.
3. **Cost:** SLA printers and materials can be more expensive compared to other 3D printing methods.

## Applications of SLA:

1. **Prototyping:** SLA is widely used for creating high-resolution prototypes in automotive, aerospace, and consumer goods industries.
2. **Jewelry and Art:** SLA's precision and smooth surface finish make it popular for producing intricate jewelry and artistic pieces.
3. **Dental and Medical:** SLA is employed for producing dental models, surgical guides, custom prosthetics, and anatomical models.
4. **Engineering and Product Design:** SLA enables engineers and designers to iterate and test designs before mass production.
5. **Microfluidics:** SLA is utilized in fabricating microfluidic devices for biomedical research and diagnostic applications.

Stereolithography (SLA): Advancing Precision and Detail in Additive Manufacturing


> Fused Deposition Modeling (FDM) is an additive manufacturing process that utilizes a thermoplastic filament as the printing material.

## Understanding the FDM Process

The FDM process involves the following steps:

1. **Digital Model Creation**: FDM begins with the creation of a digital 3D model using computer-aided design (CAD) software, usually saved in STL format.
2. **Slicing and Instruction Generation**: Specialized slicing software breaks down the 3D model into thin layers, generating instructions for the 3D printer. Parameters such as layer thickness and infill density can be adjusted.
3. **Printing Material and Filament**: FDM printers utilize thermoplastic filaments like Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA). The filament is loaded into the printer's extruder system.
4. **Melting and Extrusion**: The printer heats the nozzle, softening the filament until it becomes molten. The extruder system pushes the molten filament through the nozzle's small opening.
5. **Layer-by-Layer Deposition**: The printer follows the slicing software instructions, depositing the molten material onto the build platform or the previous layer. Each layer solidifies rapidly as heat dissipates, adhering to the previous layer.
6. **Support Structures**: FDM printers can create temporary support structures for overhanging features, minimizing the need for manual post-processing.
7. **Post-processing**: After printing, the object may require post-processing, such as removing support structures, surface sanding, and additional treatments like painting or coating.

## Advantages of Fused Deposition Modeling (FDM)

FDM offers several advantages, including:

1. **Versatility**: FDM is compatible with various thermoplastic materials, enabling diverse applications and customized properties.
2. **Affordability**: FDM printers are relatively inexpensive compared to other additive manufacturing technologies, making them accessible to a wider audience.
3. **User-Friendly**: FDM machines are easy to use, with a straightforward printing process requiring minimal setup and maintenance.
4. **Built-in Support Structures**: FDM printers can generate support structures, reducing the need for extensive manual post-processing.
5. **Large Build Volume**: FDM printers come in different sizes, allowing for the production of large-scale objects.

## Considerations and Disadvantages

Despite its benefits, FDM has certain limitations to keep in mind:

1. **Lower Resolution**: FDM prints may exhibit visible layer lines, resulting in a relatively lower resolution compared to techniques like SLA or SLS.
2. **Material Strength**: While FDM offers a wide range of material options, the strength and mechanical properties may not match those of injection-molded parts.
3. **Printing Speed**: FDM printing can be time-consuming, especially for complex designs, due to the layer-by-layer deposition process.

## Applications of Fused Deposition Modeling (FDM)

FDM finds its utility in various applications, such as:

1. **Rapid Prototyping**: FDM is widely used for rapid prototyping, allowing engineers and designers to iterate and test their designs quickly.
2. **Customization**: FDM enables the production of personalized objects, including customized orthopedic implants and dental aligners.
3. **Education**: FDM printers are popular in educational settings, fostering hands-on learning and introducing students to 3D printing technology.
4. **Tooling and Jigs**: FDM can produce low-cost tools, jigs, and fixtures used in manufacturing processes, reducing lead

Fused Deposition Modeling (FDM) in Additive Manufacturing: Process, Advantages, Disadvantages and Applications



In this article, I will explain to you the first inversion of the slider-crank mechanism which is used in the engine to rotate the crank, as a result, the wheels of the vehicle rotate.

But before trying to understand this concept you should have some knowledge about kinematic links, kinematic chains, kinematic pairs, and a four-bar chain. These concepts are very easy and should not take more than 20-30 mins to master. I will try to write about these topics soon in other articles so stay tuned. But as of now, there are many resources on the internet where you can learn concepts of kinematic links, kinematic chains, kinematic pairs, and four-bar chain. So go ahead read that and come here to learn about the slider-crank mechanism. I have also included two CAD models to help you understand better.

## Slider-Crank Chain

It is a four-bar chain with one of the turning pairs replaced by a sliding pair. Or you can say: When one of the turning pairs of a four-bar chain is replaced by a sliding pair, it becomes a single slider crank chain.

A mechanism is a closed kinematic chain with one of its links fixed. We can fix any link at a time, so from the same chain, we get a different mechanism.

### Kinematic Inversion

Before learning about the first inversion of the slider-crank chain let us know what a kinematic inversion is. Kinematic inversion means that the process of fixing different links of the same kinematic chain to produce different mechanisms. The most important thing about this process of kinematic inversion is that the relative motion between various links is independent of the kinematic inversion. So as long as the chain is the same, the relative motion between various links remains the same, independent of which particular link is kept fixed.

### Inversions of Slider-Crank Chain

Similarly, by fixing different links at a time of a slider-crank chain we get its inversions.

The following are the inversions of the slider-crank chain.

1. First Inversion: Link 1 is fixed, link 2 is made crank and link 4 is made the slider.
2. Second inversion: Link 2 is fixed, link 3 becomes the crank and link 4 is the slider.
3. Third Inversion: Link 3 is fixed, link 2 becomes the crank and link 4 the slider.
4. Fourth inversion: This is obtained when the link 4 is fixed.

In this article, we are only discussing the first inversion. I will explain the other inversions in other articles.

#### First Inversion of Slider-Crank Chain

![Slider Crank Chain](https://hlwctjueumzxtrnirmnh.supabase.co/storage/v1/object/public/assets/slider-crank-chain.png?t=2023-06-04T05%3A14%3A11.424Z)

This inversion is obtained when link 1 is fixed and links 2 and 4 are made the crank and the slider respectively. The applications of the first inversion can be seen in the reciprocating engine and the reciprocating compressor. In the reciprocating engine, the piston is the driver whereas as in reciprocating compressor the crank is the driver.

To understand more clearly consider the model given below.



![Reciprocating Mechanism](https://hlwctjueumzxtrnirmnh.supabase.co/storage/v1/object/public/assets/reciprocating_mechanism1.gif)

In this model, the Plummer Block (blue color) is the fixed link 1. The crank (green color) is link 2. The piston (yellow color) is the link 4. Connecting rod (red color) is link 3 connecting the crank (link 2 ) and the piston (link 4). The reciprocating motion of the piston results in the rotation of the crank.

Here's another example of the first inversion of the slider-crank chain.

![Reciprocating Mechanism](https://hlwctjueumzxtrnirmnh.supabase.co/storage/v1/object/public/assets/reciprocating-mechanism2.gif?t=2023-06-04T05%3A13%3A58.792Z)

As you can see in the above mechanism, the reciprocating motion of the slider results in the rotation of the crank and vice versa.

The First Inversion of Slider Crank Mechanism

In this article, I will explain you all about pattern allowances and how to calculate different pattern allowances for designing the pattern for metal casting.

## 1. Pattern

A pattern is a replica of the object to be made by the casting process, with some **modifications**

*The main modifications are:*

* Addition of pattern allowances,
* Provision of core prints, and 
* Eliminating fine details which cannot be obtained by casting.


## 2. Pattern Allowances - Their Types

The dimensions of the pattern are made greater than the dimensions of the final casting product. This is because of various reasons discussed below:

### 2.1 Shrinkage Allowance

All metals shrink when they are cooled (except [Bismuth](https://en.wikipedia.org/wiki/Bismuth)). However, there is a distinction between liquid shrinkage and solid shrinkage.

To account for liquid shrinkage, risers are provided in the moulds.

**The Shrinkage allowance is provided to take care of the reduction in volume due to Solid Shrinkage.** 

Solid Shrinkage is the reduction in volume when the metal changes from liquid to solid state at the solidus temperature.

Rate of contraction depends on:

1. Material
2. The metallurgical transformation taking place during solidification.

The actual value of shrinkage depends on various factors specific to a particular casting:

1. The actual composition of alloy cast,
2. Mould Materials used,
3. Mould Design,
4. The complexity of the pattern and the component size.

#### Important points

1. As a rule, all the dimensions are going to be altered uniformly unless they are restrained in some way. For example, a dry sand core at the centre of the casting may restrain the casting from contracting but the edges are not restrained. Thus it may be desirable to provide a higher shrinkage allowance for outer dimensions compared to ones which may be restrained.
2. The pattern maker's experience and a little bit of trial are to be used in arriving at the final shrinkages provided on the pattern.
3. The shrinkage allowance is always added to the linear dimensions. Even in case of internal dimensions (e.g. internal diameters of cylinders), the material has a tendency to contract towards the centre and thus are to be increased.
4. It is also possible to obtain shrink rulers for specific materials such as steels which are nothing but special scales where dimensions are shown are actually longer by a measure equal to the shrinkage allowance. Dimensions provided by such a rule can be used at the time of making the pattern. Different shrink rulers are used for different casting materials.

#### Various Metals and Their Shrinkage Allowances

| # | Material | Pattern Dimensions mm | Shrinkage Allowance mm/m |
|---|----------------------|---------------------------|--------------------------|
| 1 | Grey Cast Iron | up to 600 600 to 1200 over 1200 | 10.5 8.5 7.0 |
| 2 | Plain Carbon Steel | up to 600 600 to 1800 over 1800 | 21.0 16.0 13.0 |
| 3 | Chromium Steel | - | 20.0 |
| 4 | Manganese Steel | - | 25.0 to 38.0 |


### Question 1

![Pattern Image](https://hlwctjueumzxtrnirmnh.supabase.co/storage/v1/object/public/assets/types-of-pattern-allowances-why-they-are-important-for-designing-pattern-for-metal-casting/shrinkage_allowance_question_wwsne2.webp)

#### The casting shown in the above figure is to be made in plain carbon steel using a wooden pattern. Assuming only shrinkage allowance, calculate the dimensions of the pattern.

From the [shrinkage allowance table](#variousmetalsandtheirshrinkageallowances) above, the shrinkage allowance for steel is 21.0 mm/m.

For dimension 200, allowance is 200 * 21.0/1000 = 4.20 mm.

For dimension 150, allowance is 150 * 21.0/1000 = 3.15 = 3.20 mm (approximately).

For dimension 100, allowance is 100 * 21.0/1000 = 2.10 mm.

For dimension 80, allowance is 80 * 21.0/1000 = 1.68 = 1.70 mm (approximately).

Therefore, the pattern with required dimensions taking shrinkage into account is shown below:

![Solution Image](https://hlwctjueumzxtrnirmnh.supabase.co/storage/v1/object/public/assets/types-of-pattern-allowances-why-they-are-important-for-designing-pattern-for-metal-casting/shrinkage_allowance_solution_flta2n.webp)

### 2.2 Finish or Machining Allowance

Extra material is provided to the pattern which is subsequently removed by machining or cleaning process because the finish and accuracy achieved in sand casting are generally low. 

This may range from 2 to 20 mm.

The type of machining allowance provided would depend on the metal cast, the type of moulding used, the class of accuracy required on the surface and the complexity of surface details. 

The machining allowance provided ultimately has to be removed by machining. Hence, the cost of providing additional machining allowance should be carefully examined before finalizing.

#### Machining Allowances on patterns for sand castings


| Dimension, mm | Allowance, mm | Allowance, mm | Allowance, mm |
|---------------|---------------|---------------|---------------|
| | Bore | Surface | Cope Side |
|---------------|---------------|---------------|---------------|
| **Cast Iron** | | | |
| up to 300 | 3.0 | 3.0 | 3.0 |
| 301 to 500 | 5.0 | 4.0 | 6.0 |
| 501 to 900 | 6.0 | 5.0 | 6.0 |
|---------------|---------------|---------------|---------------|
| **Cast Steel**| | | |
| up to 150 | 3.0 | 3.0 | 6.0 |
| 151 to 500 | 6.0 | 5.5 | 7.0 |
| 501 to 900 | 7.0 | 6.0 | 9.0 |
|---------------|---------------|---------------|---------------|
| **Non-ferrous**| | | |
| up to 200 | 2.0 | 1.5 | 2.0 |
| 201 to 300 | 2.5 | 1.5 | 3.0 |
| 301 to 900 | 3.0 | 2.5 | 3.0 |

### Question 2

![Pattern Image](https://hlwctjueumzxtrnirmnh.supabase.co/storage/v1/object/public/assets/types-of-pattern-allowances-why-they-are-important-for-designing-pattern-for-metal-casting/shrinkage_allowance_question_wwsne2.webp)

#### In the above figure, what will be the pattern dimension if all the surfaces of the casting need to be machined?

From the [Machining allowances table](#machiningallowancesonpatternsforsandcastings) above:
- Machining allowance for bore = 3 mm
- Machining allowance for all surfaces = 3 mm
- Machining allowance for cope side = 6 mm

For the dimension 80, 80 + 2 * 3 = 86 mm.
For the dimension 100, 100 + 3 + 6 = 109 mm.
For the dimension 150, 150 + 3 + 3 = 156 mm.
For the dimension 200, 200 + 5.5 + 5.5 = 211 mm.

Therefore, the final dimensions are shown in the figure below:

![Solution Image](https://hlwctjueumzxtrnirmnh.supabase.co/storage/v1/object/public/assets/types-of-pattern-allowances-why-they-are-important-for-designing-pattern-for-metal-casting/machining_allowance_bzys7p.webp)


### 2.3 Draft Allowance

![Draft Allowance](https://hlwctjueumzxtrnirmnh.supabase.co/storage/v1/object/public/assets/types-of-pattern-allowances-why-they-are-important-for-designing-pattern-for-metal-casting/Draft_Allowance_nh0ixb.webp)

At the time of withdrawing the pattern from the sand mould, the vertical faces of the pattern are in continual contact with the sand which may damage the mould cavity. To reduce its changes, the vertical faces of the pattern are always tapered from the parting line. This provision is called the draft allowance.

#### Suggested Draft Values for patterns

| Pattern Material | Height if the Given Surface, mm | Draft Angle of Surfaces, Degrees | Draft Angle of Surfaces, Degrees |
|---------------------|--------------------------------|---------------------------------|---------------------------------|
| | External Surface | Internal Surface | |
|---------------------|--------------------------------|---------------------------------|---------------------------------|
| **Wood** | | | |
| Wood | 20 | 3.00 | 3.00 |
| Wood | 21 to 50 | 1.50 | 2.50 |
| Wood | 51 to 100 | 1.00 | 1.50 |
| Wood | 101 to 200 | 0.75 | 1.00 |
| Wood | 201 to 300 | 0.50 | 1.00 |
| Wood | 301 to 800 | 0.50 | 1.75 |
| Wood | 801 to 2000 | 0.35 | 0.50 |
| Wood | over 2000 | - | 0.25 |
| **Metal and Plastic**| | | |
| Metal and Plastic | 20 | 1.50 | 3.00 |
| Metal and Plastic | 21 to 50 | 1.00 | 2.00 |
| Metal and Plastic | 51 to 100 | 0.75 | 1.00 |
| Metal and Plastic | 101 to 200 | 0.50 | 0.75 |
| Metal and Plastic | 201 to 300 | 0.50 | 0.75 |
| Metal and Plastic | 301 to 800 | 0.35 | 0.50 |


### Question 3
![Pattern Image](https://hlwctjueumzxtrnirmnh.supabase.co/storage/v1/object/public/assets/types-of-pattern-allowances-why-they-are-important-for-designing-pattern-for-metal-casting/Draft_allowance_question_doyn2v.webp)

#### Remember we provided machining allowance to the above pattern in Question 3. Now provide draft allowance to the above pattern. Take the help of the [table](#suggesteddraftvaluesforpatterns) above.

Answer: Try to solve this problem yourself and send your answers to **info@intromech.com**



### 2.4 Shake Allowance

Before withdrawal from the sand mould, the pattern is rapped all around the vertical faces to enlarge the mould cavity slightly which facilitates its removal. Since it enlarges the final casting made, it is desirable that the original pattern dimensions should be reduced to account for this increase. There is no sure way of quantifying this allowance since it is highly dependent on the foundry personnel and practices involved.

It is a negative allowance and it is to be applied only to those dimensions which are parallel to the parting plane.

One way of reducing this allowance is to increase the draft which can be removed during the subsequent machining.



### 2.5 Distortion Allowance

A metal when has just solidified is very weak and therefore is likely to be distortion prone. This is particularly so for weaker sections such as long flat portions, V, U sections or in a complicated casting which may have thin and long sections connected to thick sections. The foundry practice should be to make extra material provision for reducing the distortion. Alternatively, the shape of the pattern itself should be given a distortion of an equal amount in the opposite direction of the likely distortion direction. This can be done by trial and error basis to get the distortion amount. Some data about a few test cases may be available from the literature.





# Acknowledgements

All the information in this article is taken from the book **Manufacturing Technology (Volume 1)** by P.N. Rao.

**MANUFACTURING TECHNOLOGY (Volume 1)** relates to the practice of manufacturing with as much of scientific aspects as possible. This is a very comprehensive book on the technologies of Foundry, Forming and Welding. The book also has a separate special chapter on Previous GATE Questions and Solutions. You can also buy the ebook version from amazon. Manufacturing Technology by PN Rao PDF is available on amazon.

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Types of Pattern Allowances. Why they are important for designing pattern for metal casting?